That subreddit was taken over just like the conservative party in the USA was taken over. If you allow that to happen (both the party and the subreddit) then that's your problem. In other countries Trump would have had to found his own party, he'd still have captured a chunk of the vote but at least the Republicans that once were would not have squandered their identity. Now the house is on fire and it doesn't look like there are any mechanisms to stop it from getting much worse.

You don't let people like Trump near the levers of power if you want to keep your country in one piece. We have a similar problem here in NL and the only thing that saved us so far is that even the most rabid right winger will have to form a coalition. That still was a dime on its side and we'll see what happens at the next elections but single-issue-parties are less of a problem here, as are strongmen (though, like everywhere else, there is a fraction of the population that just wants to follow some glorious leader).