You can train a cat to live indoors. [...] It's a matter of do you have the discipline and patience to outlast their yowling until they give up and mostly accept their plight in life.

Well, yes. Just like you can train a person to live indoors - by locking them in. The word 'plight' says it.

Yes, there are risks in the outside world, but you can do things to mitigate a lot of them (depending on where you live). You can have them treated against diseases and fleas, etc.

Would you keep your kids indoors on similar grounds? I think not.