It's an interesting question, but unfortunately the answer isn't super straightforward because what one person finds supportive may be unsupportive to another. It's all very subjective, as divine said above.

I'm an admin for a large Facebook mental health group, and sometimes we have to make judgment calls. Certain things are easy to define as unsupportive (name calling, rude/judgmental comments, for example) while other things are less clear. In these cases if I receive a complaint, I'll encourage the person who made the post to take what they like and leave the rest.

Sometimes a person is looking for hugs, and sometimes someone is looking for ideas to make a change in their life. Neither are necessarily right or wrong, just different. I always find it helpful when people emphasize what they are looking for in their post so I know how to go about replying.