"This is why you always punch Nazis," redux:
Last year, Austria's version of the Republicans formed a temporary alliance with the Austrian Nazi party in order to win an election. This is the third time this has happened, so nobody was predicting a disaster; their Republicans, not the Nazis, would be the ones in charge, the ones calling the shots.
But each time, the Nazis' price for supporting their Republicans has gone up. This time they demanded control over the Austrian federal police. And they just used those police to frame, and come down hard on ... Austria's own counter-espionage and counter-terrorism police, for the "crime" of investigating and bringing charges against Austrian Nazis who had committed, plotted, or encouraged violence against leftists and minorities.
FASCISTS ARE NOT ACCEPTABLE COALITION PARTNERS. Center-right parties keep repeating the mistake that Germany's Christian Democrats made back in the '30s of thinking that they can use the Nazis to eek out narrow election wins without being, in turn, taken over by the Nazis. If the center-right party in your country makes public appeals for support from, and offers any kind of vague assurances (let alone concrete promises) to a pro-violence right-wing extremist party, THAT'S A PROBLEM. That's a serious danger for freedom and democracy, a serious risk to human life.
I don't care how much you might personally prefer center-right policies to center-left ones. Maybe you think there are too many immigrants, maybe you think taxes are too high, maybe you think unions are too strong, maybe you think we're under-funding or otherwise hamstringing our military, maybe you think we're over-regulating our businesses, maybe you think religious values aren't being promoted enough, maybe you might have any other of a dozen reasons for preferring a center-right government to a center-left government. But if the only way you can get that is by accepting fascists into your party or your coalition? You won't end up with a center-right government. You'll end up with fascism. So once your party leaders make that mistake? If you vote for them, you're not voting for a center-right party any more. You're voting for fascism.
Because whether it's Hungary's Fidesz reaching out to the KDNP, whether it's Britain's Tories reaching out to UKIP, or whether it's Trump reaching out to the Alt-Right? Once you let these people in, they immediately set about overthrowing the government. And they will keep trying until they succeed. Not until they succeed in getting elected; far-right violent extremists know that they will never win a free and fair election in any country on earth. Until they succeed and overthrowing the government, so that they can be free to murder opponents and minorities once again.
That THEY WON'T STOP AT LEGAL MEANS, and that center-right parties keep thinking they can sow the wind without reaping the whirlwind, means that on the left (and even in the center) YOU CAN'T STOP AT LEGAL MEANS, EITHER, not if legal means aren't working, not if you can see that legal means aren't stopping fascist infiltration into the center-right movement. Once the center-right party allies itself with a fascist movement, openly, you have to do whatever you have to do to stop that fascist movement from organizing, spreading, and successfully installing a fascist dictator. It's either that or flee the country, or, if you don't flee, living in a dictatorship and watching millions die all over again.