And “bringing the government down” often just means a new coalition is formed with a couple cabinet seats changing hands; multiparty proportional systems have less cabinet change as a proportion of the cabinet than duopoly systems, though they have more frequent partial cabinet changes. The dramatic langauge may be appropriate with FPTP in a parliamentary system, but is less so in a multiparty proportional parliamentary system.
And, of course, since TFA addresses particularly the democrat-republican-independent dynamic in the USA, a proportional multiparty electoral system is actually a whole separate change from a parliamentary system, and the “a 2% coalition partner defecting can bring down the government” concern only applies to parliamentary systems, even if you adopt multiparty PR in US legislative elections (even for the elections of Presidential electors) it does not apply to the US without the separate and larger change of adopting parliamentary government. Multiparty PR (using, say, STV within states) for the House and even approximately (via the safe harbor statutes) as a norm for Presidential electors is viable by statutory change, a parliamentary system would take Constitutiional change.
But, then we have things like health care, abortion, and firearm regulation. Americans largely want better/cheaper access to the first two and more of the third. Yet, we can’t get any of them.
I happen to agree with you about abortion, and thing the opposition party is and will continue to be punished for passing unpopular restrictions on reproductive health care. But one thing I don't think anybody can reasonably say is that GOP voters were bamboozled into voting for curtailment of reproductive rights; abortion and public schools are the two fundamental defining differences between the parties!
If you have a proportional voting system with 5% electoral threshold, they you don't have any 2% parties in the parliament, as the smallest possible is 5%.
Most countries with proportional systems have a threshold that requires something like 5% of the vote to earn seats. So nobody with 2% of the vote is going to be part of the coalition. Furthermore, pulling out of coalition, without a very good reason, is an excellent way to ensure that nobody wants you as a coalition partner in the future.
Yes, some countries with PR have government stability issues. So does the US, see government shutdowns, accusation of obstructionism, etc. That's just an inevitable consequence of humans disagreeing about policy.