CailinDana - I agree, Tescos' is a business not a charity. But I find their business model unethical, for all the reasons Plomino and Bochead talk about and more.
They (and others) land bank, have very powerful lobbyists. Form 'iron rings' of shops in areas to drive out any competition and they can afford to have loss shops in order to keep out the alternatives.
So there is no real choice. Every Tesco's sells the same stuff, much like any other supermarket. Just because you have the 4 big ones in your area, how much product choice do you really have? The only choice is price and it is a race to the bottom. The only people paying for this are the suppliers.
My FIL owns and runs a shop. He's early 80s and will be retiring soon. The business isn't viable anymore and he is in the process of running it down. He can't afford to stay open 24hrs - staff wages, NI, insurance etc... Nor would he want to, after all he would like some time with his family. So when you say the supermarket is convenient becauses it opens late and is cheaper than local independents - you're right. My FIL can't buy in the volumes needed to bring the down the price or negotiate with the suppliers. He can't be open at 10 at night and he can't offer you food shop, clothes, toys, electricals, jewellery, mortgages, banking etc... all under one roof. But what he can offer is excellent service, sell you the right product for you and be there if something goes wrong.