Exactly - seemingly assuming that their darling preferred party would no longer be in power, but ignoring that in a post-PR world the big parties may not even exist, and the free-market libertarians can actually have a party that represents their views in full instead of the compromise of the Tory party which has been far from the forefront when it comes to individuals rights, and the traditionalist 'stop the world I want to get off' can have their own party etc etc.
The thing is, your view can be heard more clearly in a PR system than any other, because it's much more likely you can vote for a party which actually reflects your views rather than choosing one of 3 in a big compromise. The fact that one may find themselves in a tiny, ignored minority on the other hand, is a problem which goes beyond the electoral system