I'm in two minds about this.

Mind one - It seems, on the surface at least, to be a decent idea to have to qualify to vote somehow. I'm not sure "because I exist" is really good enough to have a say in how the lives of others are run.

Mind two - It's not up to us to decide how other people vote, or why; down that path lies tyranny. They live here, and if they want to vote for X because of utterly stupid policy Y, that's their right too. I personally consider voting Conservative is an act of utter selfishness masquerading as "freedom", but I no doubt have a counterpart who thinks that me voting Labour is "trying to drag the rich down with the poor".

I think the "extremists are more likely under system Z" is redundant as an argument. Again, if these extremists get a huge vote, then it's obviously what a section of society wants to see and I have no right to tell them their vote is invalid.

Trying to create a system where the people you don't like can't get into power is gerrymandering.

For me, personally, the biggest issue in politics is lying and misrepresentation with zero retractment. Countless times either the Left or the Right has won votes with outright fabrication which was full of bombast when announced as truth, but silent as a whisper when retraction. If you shout your speeches at a reactionary-whooping-up 100 dB for 20 minutes, you should be forced to shout your retractions just as loudly and for just as long. At least that way the ruling classes will do their fucking research before spewing crap that the public laps up.