This pub also has some "guidelines" on speech.
So I believe there are some limits to platforms—for example, I don't want anyone to be able to phone me up in the middle of the night to rant & ramble, nor do I appreciate people scrawling hate slogans with glue on my front door. Nor do I want someone to jam every radio frequency with their own channel over the other radio channels.
So for me, unlimited platforming as a philosophical concept is out.
That leaves content. There are things that, for me personally, I don't wanna die a Voltaire-like death in favor of. I'm just not up to defending them. Such as vengeance porn, doxxing, falsely shouting fire in a crowded theater (or the equivalent on Pennsylvania Avenue).
So unlimited free distribution of content is also out for me philosophically, personally.
I can't categorically say that I want to provide unlimited platforming to unlimited content.
Luckily, neither does the US Bill of Rights:
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
A good law. If the press is forced to publish false statements—if Twitter and AWS are forced to host false statements—the press is not free.
It's not just that the differing underlying morality, as you rightly point out, affects our sympathy for the speaker.
It's that hate speech and harassment is itself silencing by way of its chilling effect.
It is in and of itself speech-suppressing and tyrannical.
In linguistics, speech can also be acts—speech acts. And saying "STFU f*g" is an illocutionary act with an intended and often realized perlocutionary component. As in, the speaker is trying to silence the other person, and that often succeeds.
Free speech is an obstacle for free speech.
Martin Luther's speech certainly had dire consequences.
Horrific consequences on the speech of, and even lives of, the Jewish population in Europe.
Nick Cave is a good and interesting writer even when I disagree with him, as I do with him regarding metoo, Antifa, and wokeness.
A huge component of how "hi we have free speech here" became a dog-whistle, a moth-flame, to Nazi, is to be shouldered on the right wing itself. The left wants to protect the speech and expressions of groups that the Nazi would want to extinguish or enslave.
Now, it's unknown what the consequences of deplatforming is. Many seem to believe, and this does make sense to me, that the growth of the groups would've been slower but the depths of their hatred would've been deeper. So the ultimate consequence would've been a function of the unknown extent of those two factors.
Arguably if DJT would not have had such a huge platform, for his "birtherism" lie ten years ago, we would've seen a different world today.
I think these issues are not clear cut. They are difficult philosophical questions that humanity are still working out.