Being forced to sell something is quite a bit of moral distance away from being forced to allow anyone to set up a stall in your bazaar, regardless of the products they may be selling from it.
If I wanted to buy a Confederate battle flag, it shouldn't be any more difficult for me to do so than buying a 50-star US stars and stripes flag, or a pirate jolly roger flag, or a UK union jack flag, or a North Korean flag, or a rainbow hippy peace-sign flag. A meta-merchant based out of the US should simply not be able to discriminate based on content, unless it also wishes to assume legal responsibility for those things it does allow to be sold in its marketplace. Someone, somewhere, will want to sell what I want to buy, and it is no more Amazon's place to prevent us from doing business on their general-purpose e-commerce platform than it is AT&T's or Verizon's place to prevent us from talking over their phone networks.
The instant you pull CSA flags from your marketplace, everything else becomes a de facto Amazon-approved product. Like ISIS propaganda magazines. Whoops, better ban that, too. Eventually, it reaches the point where some employee has to decide whether a fill-in-the-blanks legal boilerplate form can be sold by a merchant that is not a licensed attorney in the buyer's state.
Because if Amazon removed some offensive or illegal products, customers may rely on that when shopping, and assume that anything else bought from Amazon must therefore be legal and non-offensive. If Amazon wants to do that, fine. But do it on curated.amazon.com or only.amazon.com rather than the main www.amazon.com site. Maybe I'll go there if I only want to see stuff sold directly by Amazon without having to check that box in the search results every time.
Curated marketplaces are fine, but only so long as there is a free, uncurated alternative. I think Apple should be forced to allow uncurated stores (like Cydia) or curated-by-someone-else stores (perhaps a Google Play for iOS) for those who wish to assume the additional risks posed by such offerings. They are certainly allowed to preload their own store, and make it the default, but if I want to take my property out of the walled garden, they had damned well better unlock the gates and let me leave.
In my opinion, the extent to which the platform is completely neutral is inversely proportional to the responsibility the platform operators have for the things that make use of it. Of course, by this theory, if Silk Road had not policed its black market listings at all, it could not have been shut down for promoting commerce in outlawed goods and services.