Speaking as a gay male, I enjoy a good RE yaoi-pairing as much as I do any other m/m pairing. Whether they're original characters or taken from a movie or game, it makes no difference to me. There are characters I love to see paired-up. But of course there are some pairings at times that might make some people just think "yeah right!" (If it's a known-fact the character is hetero, or an enemy or something that makes it that much harder to believe)... Or even if it just creeps you out seeing certain two characters together, I know some yaoi pairings creep me out - Sherlock Holmes and John Watson? No thanks!
But really, it's just a bit of fun and usually the people drawing (or writing) it are excellent artists (or writers). It's another way for fans to take something they enjoy, like a character or game series, and turn it into something they'll enjoy even more...
If you don't like it - don't click it. Yes kids, it's really that simple...