Agreed it would be more democratic and nothing extreme would ever get passed. Equally very little ever gets done either. Sometimes something tough needs to be done and wouldn't under pr.
Talk the steel industry. The Tories decided to let the steel industry disappear in the uk in favour of a 10 billion investment in the uk from the Chinese. Could you ever imagine that getting passed under a PR situation? There would be enough against voters in favour of keeping the steel industry which would have resulted in the 10 billion not been invested.
I'm not saying that was the right decision, but quite often it's not all black or white and when there are those difficult grey areas, pr parliaments tend to result in doing nothing or the status quo.
It can also result in that one leading big group in order to get a policy through that they want have to do a deal with a tiny minority group eg UKIP and you get laws passed which are only supported or wanted by a tiny majority of people.
Both systems have their flaws which was why the in between system old have been the way to go but we voted massively against that.