I really like the explanations and comments on this topic so far. I will only add a few experiences to explain why I've used the block function in the past.

On a different website: I used to be a bipolar forum facilitator. One member was very unwell, even with a second dx. She became almost obsessed with me. I did my best to manage the relationship the best I could for months, but it started to stress me out too much over time. She meant no harm, but I had to cut the cord for my own wellness.

Here: A long while back, I witnessed two members harshly criticizing another for hypergraphia. The member with hypergraphia was clearly very unwell in a few respects. I was a bit hypomanic at the time, so PMd the rougher of the two trying to explain what causes hypergraphia. [I'm prone to hypergraphia, too.] That member wrote the scariest stuff in her response to me. I think she was ill, too. I had to block her because I feared her anger would intensify into bullying of me.

Another member was unwell and threatening suicide in many posts. I was triggered by it because my nephew had died by suicide not long before. Though I blocked this member, I doubt he/she knew. I eventually unblocked them. By that time, their posts were no longer triggering for me.

It's hard to know what may or may not trigger a person. It could be something very minor. The fact is, we are all here because we're dealing with various levels of stress and illness. We can make choices as to what we read. Please don't take offense if/when you are blocked and don't hesitate to block someone if that is best for you. As someone wrote above, you have to put yourself first.