I had the same issue, especially using facebook. I'd always go into those arguments without a reason.

My wife pointed out, that I don't need to do that. She questioned me about the reason I am going into those arguments with others especially the ones I don't know and I'll never ever meet.

It made total sense to me. It changed me completely. Any time I want to say something on the internet I just keep it to myself, and its great. I don't need to think 'oh what is that person gonna say etc'.

I only express opinions of my own like the one I am typing right now and it feels great.

So my advice is, next time you are about to go on an argument on the internet, think of it and if its worth your time... and just don't do it :)