I support it because I realised it's wildly unfair that the number of votes that actually count matter are the total for the second placed candidate plus 1.
I'd never advocate not voting, but the fact is for most people under first past the post it's a waste of time.
Why would a switch to PR (or the STV system, which is what the Electoral Reform Society actually advocate) lead to an increase in the number of MPs?
The only obvious reason would seem to be somebody deliberately hypothosising a system that lowers the bar to become an MP so low that they can...