if you're gonna complain, be smart about it

it seems lately i've been surrounded by people who complain just to complain. while that is, in itself, annoying, these people are taking it a step further. they're doing so in a way that it is harmful to others. whether they are putting down someone else personally or professionally, they are complaining about things they know nothing about and spreading, basically, lies about others.
this happens at school. this happens in the community. this happens online.
i heard once that you shouldn't complain unless you are looking for a solution.
i agree with that.
but now, even more importantly, i think you shouldn't complain unless you are knowledgeable about what you're saying. otherwise, you just look like a fool.