If you think so, alright then. I don't.
I think it’s OK to ask dumb questions twice. If you don’t get it by the third time (or fail to remember), then we might need to step back and revisit fundamentals, or your mental model might need adjustment so that the information makes sense in context.
Everyone sometimes screws up. Some more than others. Some distractingly so, and some so often that it's not worth continuing the relationship. But the mere fact that someone at some point screws up does not make them irredeemable. So, yes, I think cutting people slack is important.
This is totally orthogonal to being qualified for a job, or being good, or any other attributes people have that puts them out of their depth. If you work with a bunch of unqualified poseurs, then sure, slack isn't what's missing, and you should quit. But if you find yourself in that situation very often, I'd be asking different questions...
And. What if it's your customer in the room? Are you firing them for being 'stupid'?
The superclever types that thing their colleagues are stupid are often the most dangerous, as they'll just 'go it alone' and then leave when they fuck up and suddenly everyone is stupid and not grateful.
Assumptions are inevitable. They get harder to question the longer they go unquestioned. Newcomers to a group can see them better.
Perhaps cutting people some slack and helping them work better by asking basic questions is a skill we all need to learn.