heterosexual is really in the same boat as vaginal: even if we were to use them, they would be woefully undertagged (and therefore useless for most purposes) because they're the 'default', comprising the majority of sex/romance pictures on Danbooru. That sentiment may be heteronormative (which is a loaded word if ever I've heard one), but it's also true, which should probably count for something.
H-Leviathan said:
Even in images with the "yuri" tag, hetero images still appear
I just scanned through the first 10 pages of yuri and found zero males. If this is, in fact, a problem at all, it's certainly not a big one.
H-Leviathan said:
Plus, not everyone can use three tags. Some people just stick with basic, free accounts.
We've had discussions about this in the past, and the consensus is that we shouldn't add redundant tags to make Member-level searching easier. Sort of a raw deal, I know, but albert does have to pay the bills somehow, and $20 really isn't that expensive.