Proportional representation enables people to vote for whoever they like

The first past the post (FPtP) system of voting means that we have fewer political parties than we otherwise would have, and this in turn prevents the existence of coalition Governments. If we assume that the greater the proliferation of small parties, the less like 'Government' the Government becomes (due to their being a coalition, always) then FPtP prevents the erosion of, and protects the stability of the State.