In terms of posing an internal political threat to the West, I don't see it as a massive issue in most countries (there are some exceptions, though). I do see right wing populism and far rightists as a growing problem. Now, I don't think their speech should be banned, but I'd say they're the bigger problem right now. They are the fastest growing and most destabilizing force in most nations.
The problem you are seeing on the left is a collapse of the center-left parties. This is going to put pressure on the left wing to become more extreme and populist. This has yet to translate into big electoral gains for the far left in most places, but I can easily see it happening within the next 10 years or so.