I see what you want out of the blocking feature, but it can't work reliably with ActivityPub enabled on your account.
The only way to accomplish this, would be for kbin to provide a "don't federate any of my comments or posts" button, or even a personal federation whitelist, which prevents your contributions from reaching other servers where blocking cannot be guaranteed. Only then could Kbin start hiding your posts from certain users. You would also need to hide your comments from logged-out users, of course. This would also come with some database modifications that would be pretty difficult to get right.
Perhaps you could find a few programmers that share your concern and create a fork of the Kbin code, with your own server where you can attempt to apply this blocking mechanism.
Aside from the fact an alt account is pretty easy to register, you just can't implement hiding your posts from other people in a system that federates with Kbin or its alternatives.