The social networks rely mostly on network effects. There is really no way to, for example, discern, prior to a person joining a network, whether they are actually qualified to be able to participate in it. Sometimes, the network is visible, for example, a forum whereas there is a very low barrier of entry in terms of membership.
That is interesting to think about!
Your second point, I think, ties up to the first. Those people, who out of inclination, capability or training, are unwilling, incapable or unable to exert the effort rational analysis, will end up resorting to, as you say, "hide personal issues behind a show of empathy".
There is one more point I'd like to add though. In circles where a high amount of training is required, not only is it not possible to contribute in a meaningful way, but also there was no inclination for anyone to opine about others' comments. Whereas now, any statement, any remark, any comment, anybody feels that they can comment, criticize, or debate about. That is, the earlier inhibition, or should I say humility, seems to be disappearing. This is, in my opinion, is another reason for deterioration of debate and discussion.
Probably along with this, I'd like to add this quote from another comment in a different HN thread [0]. >> Cynicism tends to look smart to outside observers
Thank you for the wonderful and thought provoking discussion.