Personally I'm keeping an open mind on this one
I can see the arguments about the Mac App Store possibly distorting the market, but then I can also see that it might bring a bunch of benefits.
One thing that no-one seems to mention in all the hoopla over this is that Apple are halfway to an App Store for the Mac already with the Apple downloads listings - http://www.apple.com/downloads/ - all it's missing is a centralised billing mechanism and one-click purchase/installation.
Just a few thoughts on some of your list:
1) They've had a kill switch on the iPhone since the App Store opened, and to my knowledge there has only been one example of it *possibly* being used - even that one hasn't been proven (NDrive - some people lost the app, lots of others didn't, though). I suspect it's basically a "nuclear" option in case something nasty slips through the net, the prospect of which doesn't bother me at all considering the kill switch track record on the iPhone up to now.
2) Enough with the fart apps thing. Yes, there are a lot in the iPhone store - doesn't mean they're successful, though, does it? As for porn, what sort of porn app would be worth it on a Mac? They only really worked on the iPhone because they were pseudo web-sites optimised for the phone screen. Not really an issue on a full-blown computer. And you'll have a web browser (or two, or three) available anyway. Looks like a non-issue to me, TBH.
3) Actually, lots of developers liked the iPhone store model as it was an *improvement* on the terms of the other mobile app stores like Handango. It gives you a nicely pre-rolled way to market and sell a small app, with the billing mechanism etc all handled by Apple as part of their cut, which seems quite reasonable considering the services they are supplying.
As for the motive behind the whole thing, Apple has always been about the user experience and much of what was recently announced was about folding things that have worked well in iOS back into OSX proper. From a user's viewpoint, having a central place to go for apps that have been checked out for malware and won't mess up the system, with a simple purchase and installation mechanism has been huge winner on iOS, so they're offering the same for Macs. Makes a whole lot of sense in the context, and (at least so far) they aren't aiming to make it the *only* way to install apps on the Mac.
NB I don't think Apple are saints - they are out to make money like any big corporation, but they tend to do it by making stuff people like and find easy to use. I think this is just more of the same.