What is it lately, with people starting a 'conversation' only to jump down peoples throats if opinions differ from their own?

Everyone person on this entire planet is going to have a different opinion on breastfeeding, religion, presidents and everything else. So why start your bickering in a forum-like environment, only to yell and scream 'bullying' when people have different things to say?

I'm the first to give my opinion in a safe and structured environment, where it looks like people care or want to know what I have to say; but lately I've been a little hesitant to do that because of all the harassment and name calling I've been seeing.