Would you accept a house that only allowed furniture, food, books, electronics, devices from the company that built the house? Do you think it should be legal for a company to make a house with those conditions?
Would accept a car that could only take gas, tires, oil, electricity from the company that built the car? Should it be legal to offer such a vehicle?
You used to be able to buy a VCR and choose only to rent videos from Blockbuster video if you wanted "safe and clean". That didn't require any company making the VCR to force people to only to go their "safe and clean store". Apple doesn't need to force everyone on iOS to go to their store for you personally to continue to only get apps from their store.