I'm gonna take WarOwl's experiences here as an example. WarOwl, a "new" player to TF2 (at least in it's current day state), felt the community was all around overwhelmingly positive. Though, he did find the Casual server denizens to be quite obnoxious (though that doesn't necessarily mean they were toxic, just annoying). He very much liked the competitive community from what he experienced.
STAR_ has also had good times in this community. If he's going to boldly state that the friends he's made within this community all fall within being toxic then that's just horseshit. I mean, sure, people get competitive sometimes and say some hurtful shit but that's just competitive. It happens in every game.
In my own experience, I've definitely encountered toxic players. Though, in my mere 500 hours or so playing, for example, CS:GO, I've encountered more toxic and just outright vulgar players than I have ever in my 4000 of playing TF2 (for much longer nonetheless).
I think the 6s community itself gets a bad rap as being "toxic" just because it's more closely knit. The most toxicity I've ever experienced is actually in other gamemodes (i.e. HL). 6s players generally just want it to be understood why 6s is played; not for elitism but for a combination of good gameplay and "spectator-ability."
I'm going off on a lot of tangents that might not even be relevant to the OP at this point, but I think they're important to talk about and take into consideration. I'm tired for TF2 being flamed for things that are absurdly untrue and pandering.