PR would allow different factions to negotiate under formal rules like in other countries, where when a support party loses confidence, they topple the government and cause an election. PR of course also has whips but there's the prospect of dissenters starting their own party.
For a look at how that works follow the Danish election that's coming up in a couple of weeks. The old PM quit and formed his own party, another of the old ruling party did the same, and both look to be grabbing quite a large share of votes.