In that case, I'd say "No I categorically do not do side projects because I do not want FAANG X to own them" is a perfectly reasonable answer.
If you somehow manage to avoid signing that clause, then suddenly your side projects become potential competition for your employer, so they might get you into awkward discussions with your manager, especially so if your side project turns out useful or valuable. So having your own side project might require a level of people skills that programmers highly dedicated to their craft will likely not have.
I know people who dread "their" side projects because it just feels like additional unpaid work to them. I also know people who keep their side projects a secret from their employer.
If you select for people with corporate side projects, you're likely selecting for future employees with bad people skills.