You have classified me as "For Brexit", which I'm not…
Actually he hasn't done that at all, all he has indicated is that if there was proportional representation there would be a different split in the number for each party in parliament - effectively the Conservatives would not have a majority, and would have to form a coalition. In fact, that's what nearly always happens in PR systems.
The benefit is that minority parties get to have a say. The negative aspect is that majority parties get to have a say.
The second part is a problem when a small party gets to dictate government policy, which is what the DUP did with the May government.
While PR gives places in parliament to Green MPs, it would also give places to UKIP and Brexit party MPs, and perhaps even those further to the right. I don't see this as a really big problem, unless these parties are in a leading coalition, and can advocate for things beyond their strict size dictates. At the end of the day it satisfies a proportion of the public to have these people as MPs, so, so be it - they get what they deserve.
On the number of votes cast against the conservatives, I find it unbelievable that people couldn't work out that they needed to vote tactically to avoid a huge Conservative majority, there are no end of seats in which you see people have voted Labour and Lib Dem in large numbers, but the Conservatives still took the seat (often by just a few votes). This is because Labour and Lib Dem voters split their vote. On this point I am amazed at the number who voted Lib Dem in Battersea, when it should have been obvious to anyone that the Lib Dems did not stand a chance here.
On Brexit as a whole, what a mess. Even with a huge majority Johnson still has to move the goalposts while braying on about "healing the nation" (insisting on a trade deal by the end of 2020, removing workers rights and environmental protection from the Brexit bill). What a Berk (in the true rhyming slang sense of the word)!
Keep at it Guy, we won't win, but we can keep complaining! And it won't hurt in five year's time to remind people what they voted for.