Worth adding on that McCarthy knew exactly what he was doing and didn't care. It raised his profile. (Source: master of the senate, caro)
Those who validate dirty pool in pursuit of the greater good will always be enabling people like that.
Being moderate is a delicate balance where foes seek power in whatever way possible. With this said I get quite concerned when someone says it's their freedom to plot the end of my existence.
Look at Joseph McCarthy and see a counter-example. He used the exact same logic: that to suppress Soviet-style totalitarian government in the US, we had to be intolerant of all far left views.
It destroyed many peoples' lives, most of who were not at all sympathetic to Soviet-style communism.
Similar to your example, we could also argue that McCarthy was indeed effective at preventing Soviet-style communism in America (since the US still has free speech and there has not been another holocaust). But in both cases we don't have convincing evidence that suppressing speech was actually helpful.