As someone who believes that Brexit will damage UK society, I would argue that this is certainly not unique to proportional systems.

Eu elections are PR which is where Brexit got its start.

You right its unique its more prevalent in PR systems its only rare cases where governments don't have a working majority in the UK

That first line could mean several different things. Are you claiming that the excessive power of fringe elements in the EU is why the UK decided to leave?

From a global perspective, the UK and US are currently undergoing existential crises - arguably due to people feeling politically underrepresented - whilst many countries with a strong PR such as Finland or Switzerland seem to be functioning better.