I think this whole “Not all!” argument can be sidestepped. From what I’ve read and seen and talked to people about, the “Not all!” comes from ignorance. A lot of people don’t understand the concept of institutional racism. Most people probably wouldn’t even consider the idea in their lives left alone.
Maybe there’s a good reason to redefine racism as institutional racism. I haven’t heard that reason yet, so my view on the matter is that when talking about institutions of racism, progressives (because only progressives really talk about it) should be explicit about the institutional aspect. If I’m wrong, which I very well could be, I’m happy to be educated why.
If we allowed “racism” to simply mean racially based discrimination or dislike, then I think this opens the door to real discussion with those being called racist. When someone is just called racist in a blanket statement, they shut down, and don’t want to know what you mean by it because they already think they know. So if we tip-toe around using “racist” as much as progressives tip-toe around pronouns then there’s a clear path to educating others.