I'm being more philosophical I think
my point is more to do with what is now seen as not only acceptable but quite appealing.
I'm of an age where anal sex was pretty much unheard of, now nearly every bloke wants to stick up a girls arse. I've never done it but the appeal is certainly there. The idea that having a FFM threesome is readily on tap and ,up until a few years ago, was never as readily available to the masses as it is now. Girls kissing girls for "fun" is becoming ubiquitous. It's almost expected that girls now should fuck like porn stars. This is all with the rise of Internet porn of course. Kim kardashion, Paris Hilton, the X factor girl have, unintentionally, made porn sex quite acceptable. May main point after reading the OPs original dilemma and the subsequent replies are where does it stop? Open conversation amoung "heterosexual" men about the total acceptance and encouragement of a gay sex act makes me wonder.
Where does it stop, you ask. A great question and there are a lot of points I could make and will try to make a few.
Does it need to stop? As my kids frequently say to me "welcome to the 21st century" I think this is just a natural progression of people wanting bigger and better experiences. Take stag and hen dos, (correct plural?) nowadays it's the norm to have at least 2 and one of those is usually abroad somewhere, 30 years ago I went out for a couple of pints with a few mates the night before. Phones, all the hype about the iPhone 6 then it'll be 7, 8, 9 etc, it's just a bloody phone, I managed perfectly well without a mobile for 40 years. Then eating and drinking, it's all about "craft beers" and micro breweries and eating exotic foreign food, "Oh, this town is crap cos it doesn't have a Nepalese restaurant" etc etc. Even the flavours of crisps, when I was a lad there was one flavour, Smiths - with a little blue bag of salt inside, now there's Aardvark & Anchovie, Somerset Farm Cheddar and Organic spring harvested Chives!
Now, all this may sound like I'm an old fart who doesn't have time for the modern world. Not a bit of it, I just involve myself in the bits that I like and ignore the rest.
As to your original question, where does it all stop regarding sex. A particularly virulent incurable STI might make a few people stop and think or maybe this will herald the end of civilisation as happened with the Roman Empire, they knew a thing or two about orgies.
Going back to guys sucking cock, I guess it depends on whereabouts you are on the spectrum. I have never believed that one is either gay or straight, more like 100/0, 80/20, 70/30, or even 50/50, so your reference to "heterosexual" guys will include all those variations. There will be some who are totally repulsed by the idea, those that are quite happy to give it a go and others somewhere in between. For me, a lot of the excitement is because of the fact it's a bit taboo, the frisson of doing something "naughty" if you like. There again, so is punting with women, most members of society would be appalled at our behaviour and is Class A divorce material for sure.
Going to stop now as I've spotted enough bollocks, I think.