Mr. Statistics Teacher, what are you talking about exactly? It's not insane to compare a mean over 5% of the population versus a mean over 95%.

Or are you suggesting maybe somebody sampled 1000 people at random and averaged whatever 40-60 gay people they got? That would be bad practice, yes.
It turns out (in statistics class) that if you are trying find out how many people have some characteristic (like being a drug user) by randomly checking only some of the people you won't get exactly the right result. For instance, you might accidentally call only drug users, and think that 100% of the population are drug users. It works out, though, that if you do the experiment a bunch of times that the error in the count is about the square root of the sample, on average.
So, for instance (I am completely making up all the numbers except the square roots), if you call 10,000 people and 10% are LGBTQ, or 1000, and of each of these groups 10% are drug users, then then the number of non-LGBTQ people who say they are drug users is 10% of 9000 or 900 plus or minus square root of 900 which is about 30 or 3%. Of the 1000 LGBTQ people the number of drug users is 10% of 1000 or 100 plus or minus square root of 100 = 10 or 10%. So even though the fraction of drug users is exactly the same in both groups for the full population, the measurement error for the smaller group is 10% instead of 3%, and you are likely to draw a bad comparison comparing the means.
Wow. I like pegging. I like submissive dudes. But I would NEVER anally rape someone, unless they specifically asked (in which case it wouldn't be rape). If a guy asked to be pegged once and then didn't ask again, I would conclude that he didn't enjoy it after all. Or, you know, I would ASK him. And even if he said that he was, generally, up for just being taken by surprise, I'd ask for some sort of signal word first. Even people who really like anal are sometimes not in the mood for it due to inconvenient digestive issues, or they want to clean up first. Don't project your fantasies -- and they are fantasies; fantasies don't involve constipation, reality does -- onto every peggee in the world.
I don't know what people are getting worked up about. No anal rape is going to happen tonight. I think any guy who has expressed an interest in Pegging would love to have his girlfriend either bring it up suggestively or show up with the proper equipment.

Guys don't have to worry about being overpowered or something like that happening non-consensually. Guys do not have any issues about saying no to something they don't want to do

I could see the concern if you didn't know the difference between men and women. I'm sure there are some women who would go along with something when she didn't want to. But no guys going to go along with this and no woman could never overpower guy enough to do it. Of course there is a one-in-a-million situation where a guy is really passive and the girl is really strong. But clearly in that case the participants would know and proceed accordingly.

Nobody's talking about the girls actually forcing themselves on a guy. They're talking about pretend. Anyone that doesn't get that it's very out of touch or being intentionally obtuse. Frankly I think this is something a lot of guys might be hesitant to ask for. Girls can freak out thinking a guys gay. Or it could be a big turn-on for her or just seem weird. Women often have a lot of expectations of a man to maintain a masculine persona.

If a guy has expressed an interest, be good giving and game and encourage him and propose it. If money is not a big issue, buy the equipment but I guess if you're not fairly confident he'll be into it you don't want to waste your money
There's quite a difference in 'I did it a few times and had a great time, I'd like to make it part of our funtimes', and 'I dunno, saw it in a porno once, guess I'd like to try it'. Both are expressing an interest, yes? We don't know exactly how it was mentioned, whether the guy seemed enthusiastic or just curious. And of course guys can get overpowered, or sometimes agree to things that they're not fully on board with. If she's really gung-ho about it, he might decide to go along even though he's not really feeling it, and yeah, people get hurt that way - either physically or mentally. This is why communication is so dang important. Talk about what you want in clear and unambiguous terms.
rpsf @4
Guys don't have to worry about being overpowered or something like that happening non-consensually

Of course that could happen. What about when the guy is tied up during kinky/SM play, for example?
Getting surprised with some lingerie, or chocolates, or a toy you both think is pretty hot? I'm having trouble seeing a downside.
RSPF @4: "Guys do not have any issues about saying no to something they don't want to do"

Really? You might want to ask Sportlandia about the pressure he's felt to say yes to women who wanted sex when he did not, with threatened (and actual) consequences of being called gay and having nasty rumours spread about him. I know you're talking about specific acts and physical force, but psychological coercion is not limited to any gender.

Quincunx @7: Surprise eight inches up your ass is a bit different from lingerie and chocolates!

That leads me to another point: If this guy is a newbie, size matters. Another reason they should pick out the toy together, and practice first, consensually.
@8 - That's a point I meant to make also. Lots of guys need a bit of training up before they can take anything substantial up there. I have a set of smooth toys in graduating widths that I use on my play-partner before bringing out the realistic dongs.
Of course you can find extreme examples. Tied up. No one is suggesting she tie him up and force him while he is desperately trying to get loose. Forced under threat by an evil woman. But that is not what we are talking about. It would be extremely rare for a man to be pegged with the woman accidentally doing it against his will. And we are not talking about an evil female rapist using mental coercion. We are talking an infinitesimally small risk if that, if she bought a strap on and introduced it into play. And guys don't bring up pegging because they saw it in a porn once and were just passing curious. A guy who brings it up at all is interested. It is way too subversive and threatening to a guy who is not actually interested. But of course, any "taking him" would be done with an active awareness of response and feedback. I suppose seeking verbal consent can be used. But not necessarily. Any guy who doesn't want to be pegged is going to be pretty actively giving non consent
And for the record, this is what the questioner said. My boyfriend keeps talking about how much he would like for me to peg him. Seems pretty clear.
@3 "Fantasies don't involve constipation, reality does."

I want this in needlepoint and I want it displayed prominently.
I have a lot of problems with the pegging reader advice. Here are a couple of them: 1) What this man needs to understand -- and I speak from personal experience as a woman who has sought the experience and who has had men seek the experience from me -- is that there are a variety of things people are interested in and his specific penetration=domination/punishment/role-reversal fantasy (is that the role he always plays when he's not being pegged??) isn't The Universal Reason.

2) Asking and expecting someone who has never done it before to strap it on and magically do amazing things to someone who has also never done it before is unlikely to go as well as he's fapping. Figuring out a secure, comfortable harness arrangement and finding a dildo that's substantial enough to not bend in half at the slightest hint of resistance and long enough to allow maneuverability while being beginner friendly at the same time is tough. She can't feel the dildo itself, requiring feedback from the peggee especially while hands-free or when visibility is low. If there are size differences between partners, some go-to positions don't work as well in the reverse. Sometimes there's a learning curve for one or both parties and it takes a few practice rounds before the mechanics are mastered enough to bring in role play, domination/submission, etc.
Ankylosaurus @13: Excellent points. We've touched on issues connected to his possible lack of experience, but not hers -- and you just cannot fuck an arse the same way you'd fuck a vagina, which is something she is not likely to guess, and he may not know how to explain.