I like the fact that Facebook can't pull their apps from the store, put them on a rival store with lax standards, or otherwise circumvent the app store controls. These controls clear benefits for me, but side loading and alternate stores would cripple their effectiveness. In fact crippling the effectiveness of these controls is the purpose of side loading and alternate stores.
If you want a phone you can root, buy one. There are options out there. Why do you want to take my choice away from me?