Whilst it is possible to see Germany as having had a stable governmental system despite PR, in most other countries it has caused substantial instability, to the extent that in many countries PR is tweeked to reduce its impact, e.g. Greece where the party with the most votes gets an extra tranche of MPs. By contrast Belgium's record of 18 months without a government as a result of PR should be a warning to us all.
Is that an indictment or an endorsement?
The great virtue of 'first past the post' is that it forces parties to appeal to a wider group than their obvious supporters; know nothing tea partiers mashed up with business advocates are lined up against a mixture of union placemen and minority activists. The process of coalesce has got to occur somewhere; the belief that it is best done in the spotlight of publicity of the floor of the legislature is somewhat unproven, at best. Certainly the collapse of both the Weimar Republic and the French 4th Republic are usually blamed on their use of PR; I remain to be convinced its the optimal solution.
That sounds more like an indictment of democracy itself. I'll point out that if Wilhelm had remained on the throne of Germany, neither the collapse of the Weimar republic nor the subsequent unfortunate events would have been possible. Those are entirely the fruits of democracy.