Well, thanks for giving us something to talk about...
First, well, it's not *just* May. See, here we talk about characters that, at the very least, we'd call our 'favorites'. It just so happens that the primary source of our interests was the 'love' part. Thus, this thread tends to attract people who are so interested in one character that they honestly want the character to be real so that they could at least talk to them, if not more. It's sorta like wishing a famous movie star or pop singer was your boyfriend/girlfriend, except that we pretty much accept that, since those are not real, it's all our hearts' desire and nothing more.
Thus, the comparison to 'May fanboys' is a bit wrong. The May fanboys only like her because they think she's hot. We like the characters we like because they're our very favorite characters and we like them.
As for the question, yes, we do get a fair bit of flamers. Check the first couple of pages, for starters.
Thing is, even if we like the characters, it's not as taboo as with a Pokémon because, well, they're still human. They're just not real, like a photograph of a person. Would you say it's wrong to like a photograph of a person you like, if you like them both?
The only difference between us and other people is that we can't meet the real person, so we have to make do. Most of us are pretty rational, anyway.