I have a rule not to be involved in every thread, usually concentrating on just 3 or 4. As a rule, I tend not to get involved in "Oh isn't it terrible" kind of threads. I do think the Berlin attack is terrible, but to conclude that I do not care because I have not involved myself in that thread is a mistake.
I do make exceptions such as ymb's "Isn't it terrible" thread about the children suicide bombers. I got involved in that, not to be outraged or to virtue signal, but to point out something that the OP had missed, namely that the UK Government are actually supporting those vile people in Syria.