[carlosjobim]

Every European parliament will form into a "government" bloc and an "opposition" bloc after the election. Right wing / left wing doesn't necessarily have anything to do with it. The US congress does manage to make bi-partisan bills. Because members of congress can go against their party sometimes. In European parliaments that kind of behaviour usually results in a crisis of government and a vote of confidence.

> or they face a more moderate party taking their seats

That's not right. You cannot lose your parliament seat in any European parliament until the next election. If an MP or an entire party in Europe is too divisive, they might not be able to be part of a majority and they will be in opposition.

In the USA, the executive government is not elected by parliament - so you're comparing apples to oranges. The president builds the executive government after being elected by the people in the states. That's something different.