Well, it depends very greatly on whose definition of "harassment" they're going to use. There are plenty these days on the SJW left who define "harassment" as pretty much any public statement that disagrees with their views or challenges them in any way.
If they're just going to ban direct threats ("I'm going to kill you!"), doxxing, calls to violence ("We should go burn this guy's house down!"), etc. then I doubt most people would object.
If they're going to ban anyone who says "I think we should deport illegal immigrants" or "I support a border wall" that's a VERY different story.
It's also a very different story if they decide to get into the business of deciding what ideas and news are worthy and which aren't. One man's "conspiracy theory" or "fake news" is another man's "story that the mainstream media are ignoring, but shouldn't be." Right now, other media companies like Wikipedia are already beginning to ban "fake news" on the right, but not on the left. You can learn all about discredited pedophilia claims against Donald Trump, for example. But search Wikipedia for the equally dubious "Pizzagate" and you'll see that it's been blocked as "A conspiracy theory falsely claiming the existence of a child trafficking ring". It's that double standard that people are worried about.
It's hardly a secret that most of these media companies are located in SJW-central Silicon Valley and that their leadership skews radically left. So you would have to have your head buried pretty far into the sand to buy into the idea that they have any intention of applying their new censorship policies fairly.