https://en.wikipedia.org/wiki/2016_Batley_and_Spen_by-election
It lets people know violence cannot change the balance of power.
Even just a primary...
Your pick comes in second place, if you get the one from your own party that made it to the general, your first pick is now guaranteed the office.
Like, great sentiment, but I think the reason it works in the UK, is 99.99% of the population can't get a high powered rifle in an afternoon.