Well people can be tricked into sideloading apps if it’s possible.

To be clear I’m totally on your side and I think that’s a ridiculous reason to not have an open system, but let’s not pretend it’s not a possibility because doing so harms our otherwise very solid argument

It is definitely a possibility, for granny like I pointed out. Not for this person, who is aware of the risk and does not want to side load apps.

Like I said, they would have to somehow forget their own beliefs. Doesn't seem likely to me.