I find it strange that animegaf could be considered mean these days, considering it was pretty much a 15 person chat thread in the peak animegaf days from like 4 or 5 years ago and we'd run through like 4 OTs by just trolling each other.
Didn't K-On GAF basically spawn from that period because half the thread hated K-On? lol
What people consider 'mean or 'toxic' is very much a matter of opinion.
There are certainly specific incidents wherein a specific poster comes under a lot of flack that appears to be more personal than critical. However, I don't seem to see that happening too frequently.
On the other hand, there have always been people in this (and other) places where anime is discussed who find sustained, strongly argued criticism to be "too much". They aren't really interested in engaging in a substantial amount of sparring to defend the content that they watch - they just want to generally chat about anime without things getting "too heated".
I don't think there's anything wrong with just wanting to casually chat about anime. It's just a fact that those posters are mingling with far more critically minded who are used to getting into serious discussions about anime. It's when these two kinds of posters cross paths on a certain anime that you have problems.
The more casual poster suddenly feels like they are getting attacked and harassed for just having an opinion, while the critical poster can't understand why the casual poster is being so sensitive. These "crossover points" tend to occur around shows that
everyone (both critical and casual posters) are watching, such as
SAO,
Attack on Titan,
Erased,
MHA etc etc. This where you find the most hurt-feeling and perceived persecution.
Of course, people also flip around on how they react to different shows, so that a critical type poster who knowingly washes a trashy show isn't likely to start writing essays explaining why its trash. They know its trash and they're purely watching it for entertainment.
Obviously I'm being somewhat reductionist, but you get the idea.