“One other nice thing about FPTP is that it satisfies the participation criteria: it’s always better to vote honestly than to not vote at all.”

Except I live in a region that’s dominated by one party. I always vote of course, on principle, but my vote has never mattered because they’ve returned the same MP for the last 15 years, always with a comfortable margin. That MP has no incentive to listen to local people, because it won’t affect their future electoral chances at all. It may be that if all the disenfranchised voters actually voted together they’d overturn that; but it’s unlikely. It can be hard to persuade people that voting matters when their vote isn’t represented at all.

The pros and cons of voting systems aren’t in how mathematically correct they may or may not be, but in how it affects human behaviour. A more fair voting system would engage people in politics, and would encourage politicians to care about the people they represent.