Well, in terms of sexual things, like clop, I really don't see how that's a "Negative". Sex isn't a bad thing, it can be when done irresponsibly without a thought of the consequences, but it's not a "Bad" thing. I don't see why everyone thinks it ruins the "Happy, optimistic" nature of the show, as if sex somehow corrupts everything. That said, it obviously shouldn't be a topic brought up in the show itself, since the show is supposed to be appropriate for all ages. But it's a fine thing to bring up in fanworks, whether for story reasons or just for "Fun".
As for Gore and Violence, it has it's place. I can enjoy it at times and other times I can't. Just like with anything sexy it should be tagged and put into it's proper place, and as long as that rule is followed I have no issue with it, some people like that stuff, occasionally even I do.
I personally enjoy some adult content from the fandom, I won't go shouting it from the rooftops for no reason, but I'll bring it up with no shame when it's relevant. At times it makes me feel a bit strange, with the way people use words like "Clopper" I feel as if I'm thought of as something separate entirely. I like the show for plenty of reasons, the colorful characters, catchy songs, good morals, smooth animation all appeal to me, and I love the show as it is, no desire to push anything "Adult" into the canon material. I just also like adult fanworks too sometimes...