This blog post by Gruber is probably one of its best. He annotates Apple’s publication regarding Anti-Sideloading White Paper. You may disagree with him (I do agree with him), he points to very solid arguments.
By having side-loading available, I can already see a bunch of lazy-scammy developers who will skip the App Store because, you know, it’s a pain in the ass to deal with these app reviews… so let’s drop a bin file with a download link on a Facebook page, that should be just “good enough”. Oh and clusless IT guys who will require those apps to be downloaded because, you know, they are mandatory for this or that… schools would probably be the first in line…. wake up guys, we don’t need this shitty world.