I think it is very possible to speak plainly and even rather assertively without actually devolving into personal attacks and abusive tones, and I don't think it's too much to ask. I would even suggest that it would be better for everyone if we could all just be a little bit nicer.
Example from Linus:
This code is GARBAGE.
A better way to get the same point across:
This code does not make any sense to me.
I think it depends on the definition of "understand" in this context. In my example I used the words "does not make sense", but I did not quantify what that meant.
It could be interpreted as making sense in the context of doing things in a way that's acceptable to him.
If that doesn't "make sense" to you either, feel free to insert whatever other wording gets your point across, but I think you understand what I'm trying to say, which is that I think there is still room to be much nicer than Linus currently is, without losing the intended effect, but at the same time also not angering near as many people for (IMO) unnecessary reasons.