In discussions, people skills are very important.

I think that the allies were right because...

Is fine. As is

I think they were wrong and a better solution may be...

However

Liberals are a bunch of twats
You are all right wing warmongers
You don't know what you are talking about
or
You made that up

Are examples of what not to do.

We are never going to convince each other of anything in here nor, if we did, would it make a great global difference. Once you have put up your views, leave it at that. People may agree or disagree but they are your views and you think they are right. Whether they are or not!

Just my 2p.