Software freedom, at least for end users, is a smokescreen, too. I can revert your argument: "you want more ransomware because of a few OSS enthousiasts?" What we need is a way to curb the excesses, such as high entrance barriers to the store.
A phone/tablet is a tool, with very intense usage, and huge privacy value, not an engineer's toy.
The real smokescreen is this freedom vs security false dichotomy. If you give up freedom for the promise of security, you get neither. Look at the App Store. It's full of harmful garbage designed to extract value and waste your time by any trick necessary. It's one step short of ransomware. Oh, unless you use an app for your important documents, then it comes under new management and demands you start paying monthly or lose your stuff. Suddenly that lack of freedom to continue using an old version of the app or to dig around its internals and pull out your data becomes a loss of security. It's fine though, because this type of ransomware is totally legal and inline with your benevolent platform dictator's policies.
Your argument falls apart when you consider iPhones' 60% market share. People have spoken out about whether they want dangerous, uncontrolled third-party apps on their phones.
This is called the tyranny of the majority, where you're arguing that because most people don't care about freedom, therefore freedom doesn't have value. It's not a sound argument, much like saying freedom of speech doesn't matter because most people have nothing to say.
Editing to add: it seems particularly ironic that you think iPhone users make great purchasing decisions when they buy the phone, but are incapable of making good decisions when selecting software. What accounts for the discrepancy?
I don't care about what the riff-raff think, it is morally wrong and defies human freedom and dignity to require everyone walk around with a locked-down surveilance device in their pocket in order to function in the economy.
60% of society could be raptured tomorrow and the world would be better off.
Just in case you unironically don't understand this and aren't just playing it up:
Allowing third party installations does not mean uncontrolled third party apps. It merely means users have to option to install software on their phones - which continues to limit the softwares capabilities until the user was prompted to allow each.
You could argue "but a braindead person can randomly go on a phishing website, randomly download some .app file and suddenly - through magic go through a theoretical installation dialog to finally explicitly grant this malware problematic permissions... And I'm sure there are going to be people that will do exactly that... But without it, they'll still manage to do the same to the same effect, just without the app installation by inputting their bank credentials in a phishing site or similar
The thing your citing as a problem solved by disallowing app installs isn't actually solved - and it would not become more problematic either.
Finally, the fact of the matter remains that almost nobody would actually use the capability to install from third party stores, as you've correctly insinuated. But if anything, that should be another proof that allowing third party installs doesn't reduce security.
People just like to have everything provided to them from a single source, and will usually pay a premium for that.
Most people are stupid and short-sighted. Pointing to the stupid in support of your argument doesn't help it.
And, the app store does absolutely nothing to prevent "dangerous" apps. Apple doesn't review the code. In fact, if your code is reviewable, it's even harder to get it on the app store.
At the end of the day, the App Store and Play Store are filled with adware, spyware, and other malware - because Apple and Google like it that way. That's what they want. They don't give a single flying fuck about your security. They care about extracting 30% while simultaneously doing as little as possible. That's completely at odds with security, yes, and they know that. They just don't care.
What point are you even trying to make? That's not a counter-argument unless you assume that people in aggregate always make great purchasing decisions. Wait until you hear about cigarettes, heroine, slot machines, snake oil, tulips, and the rest of the effectively infinite list of fun and unique ways people make terrible choices or are bamboozled into acting against their own and others' interests. This is a comment thread about protecting people from scams. The premise acknowledges that people make widespread poor decisions. Is it so unthinkable that buying an iPhone is one of them?
A phone/tablet is a tool, with very intense usage, and huge privacy value, not an engineer's toy.