Yes, this behavior should not happen on a mental health site, I agree. While it might be considered as an expected/average behavior on Facebook, it definitely does not belong here; however, you cannot control their actions but you can put them in the ignore box.
If they are doing this to you, it is likely that they are doing it to other members. In any event, when a member displays such behavior, I put them ignore and I do not engage with them.
You stay true to your heart and mind, engage with those who genuinely care and love. These is lots of good support and wisdom on PC; most people carry intense suffering yet they wake up each morning and fight. Engage with those who carry a classy heart and ignore those who chose to remain mediocre.