I don't care about 18+ stuff. It just seems pretty normal to me that sexual and other adult themes pop up when you have adult artists making stuff for an adult audience. I know of very few artists I can say for certain who have NEVER drawn anything even remotely suggestive. Look in the portfolios of even Disney artists and you will find that when their audience isn't children, they do not shy away from adult themes.
What does bother me is the lack of consideration some (not all, not even most!) NSFW artists have towards those who may not care to see that particular subject or towards websites that do not allow it. Recently I came across some whiny Tumblr posts because someone learned they couldn't post their cub stuff on Weasyl. Then there are the people who don't tag appropriately and then harass people when they complain. There are the people who put suggestive images or use a cropped portion of an NSFW image for their avatar, not only on FA, but on non-furry sites like game forums. And there's the individuals who wear their modified (at risk of being too explicit) suits to cons, despite having [http://www.anthrocon.org/rules-conduct#rating]rules[/url] against fetish suits/gear in public places. I guess if it's covered in enough bacteria-promoting fibres it's alright.
The people who take it too seriously also bug me. Okay, wear a collar and tail in public if it makes you comfortable. Write lengthy forum posts on the faults of the fandom. But outside of special circumstances you should be able to step back and laugh at the fandom. A critique on the fandom isn't an attack on any person specifically. Yeah, some people make a lot of friends and even meet their partner through the fandom, that's awesome, and I did too, but that still doesn't make furry some sacred precious thing immune to criticism, because hey, people do that everywhere! If furry didn't exist, maybe they'd have been exposed to social situations through the wrestling fandom, it doesn't make wrestling less ridiculous.
At the same time I dislike the people who are pointlessly mean to others over stupid junk. So some kid wants to wear a collar to school? As long as he's happy and it doesn't get in the way of his life, who cares? Oh is he going to hurt the poor fandom's reputation? So what. I don't think people's choices need to be understood (heck I don't understand the people who wear furry gear everyday!), but they should be accepted unless they impact others and/or prevent the person from functioning in their daily life. If you don't agree with what somebody's doing, either find a way to give them advice politely or get on with your life.