I think you are missing the social and political implications of your choices.
Its not just about being a monopoly in the economical sense, which is bad per-se, but to let a private company to control what you have access or not based on particular moral, political views.
To forbid you to access technology that can compete with what they offer on the basis of "security".
If you do not get it, they control the only app store allowed where they also control what you can or cannot access to. You are implying they are good actors somehow that are doing all this thinking on you, while in reality they will do whatever they can to maximize their profits, and as long as people like you are fine with it, nothing will change.
Your current government might yet be democratic enough as this can not YET represent a threat to your civil rights or the ones you love, but things changes constantly. (Who could have predicted that the 30's Weimar Republic Germany would fall like that?)
Once your government do not respect civil rights anymore the way it should, a private company with this amount of control on your digital life can represent a big threat that unlike in the past, would be pretty hard to get rid of.
What about the concept of digital property?
Should you have choices?
Can a private company bar your choices?
Can a private company own the things that were bought by you and are in a phone that you have pay for?
Imagine if after having bought a vehicle, Wolkswagen could tell you who can you transport: "We dont allow dogs in OUR cars".
Now imagine someone saying: "I like what Wolkswagen do, its for my safety, dogs will damage my car".. "Just buy a Mercedes then!"
Or what if Wolkswagen did also sell vehicle parts, and even if you know there are pieces for your cars that are better or cheap, you wouldnt be able to buy them because the stores would be closed for you.
But then you would say: "But apple dont bar me from buying apps, i have choices.." and its a illusion of choice, because the apps were not even allowed to enter the store in the first place.
So there's a real danger into letting any private company to choose things for you before you are able to choose them.
We should have by now a good legislation about digital rights, digital property, etc, that could regulate this source of thing.
Because as i've witnessed here in the comments, you cannot let people on their own, because they can be emotionally manipulated into want things that will harm them and their rights in the long run.
It should not be just about being good for you at this particular moment, we should always take into account the collective and social implications of our choices.