I voted no too.
Small tanks do have their uses, many of which have been mentioned already.
The biggest problem is how the tanks are marketed. Small tanks are generally marketed as being great for kids to keep goldfish in! It's up to the LFS's, and supermarkets to be more responsible about the advice that is given about the tanks and the fish that they sell.
We know the Tesco tank is horrible, but it is made worse by the advice about the fish that can be kept in them. Someone on the advice given on the website will try and put a couple of comets in there, and wonder why they look cramped, or die within a couple of months (i'm being generous here, it could be weeks.) That said, an experienced fishkeeper could use it for culturing live foods, snails, shrimps etc. And have it look vaguely interesting at the same time.