Fptp is either helpful to the govt or equivalent to pr

If there is any difference at all between fptp and pr then we can say that pr tends to result in coalitions... at least to a greater extent than fptp. If it does not then pr is largely equivalent to fptp. The pertinent difference between the two systems is that anyone can get elected under pr whereas with fptp only members of the one of the established parties have a chance. We know that fptp (often) results in government... if fptp doesn't tend to result in (non-coalition) government then (again) there would be no difference between the two systems. A tendency not to result in coalitions is a tendency to result in (single party) government. The only reason to oppose pr (from the standpoint of fptp) is to protect the government... if there is a difference (and a reason to oppose pr) at all.