Anyone who argues that all users must be herded into a walled garden in the name of security and alternatives are not acceptable is essentially advocating a digital nanny state.
That is the herpes of the Linux world. That is one of the worse things that someone can suggest to install something.
Is it a bad idea? Maybe, especially if you're not technically versed. Does that mean we should take everyone's freedom to make their own choices. "because we know what's best for you"? I don't think so.
I believe that most non-technical users are self-aware enough that they stick to curated app-stores of their own volition.