Is ISIS dangerous and deplorable? Sure. Are there ideas so dangerous that they do not deserve to be exposed to public discourse and judged on their merits? I don't think so.
I would oppose the government censoring ISIS; however, I would be proud of any company that refused to to business with them.
I don't think they're choosing to give anyone specific a voice. I think they're choosing not to make judgement calls.
Once you start blocking anyone, you've weakened your ability to refuse to block others. You'd see greater demands for blocking Wikileaks, censoring articles like https://en.wikipedia.org/wiki/Illegal_prime, enforcing Europe's right-to-be-forgotten, etc. on the basis of "well you were willing to block ISIS".
I would argue that the moral dilemma is different if you choose to allow ISIS traffic to pass through you, vs have them as a client.
For paid clients, I might be more sympathetic to the argument, but even then the (moral?) rules (for nonbusiness) are incredibly tricky to figure out and keep consistent. Selective enforcement is bad for everyone in the uncertainty it spawns.
Ever heard of this little thing called abuse reports?
I wonder why you oppose government censorship, if you applaud private businesses achieving the same effect? Certainly your reasons cant be the same as the post you're replying to[0], and so you're missing their point.
[0] in particular Are there ideas so dangerous that they do not deserve to be exposed to public discourse and judged on their merits? I don't think so.