C'mon the Tesco!
There are worse things in life.
I think for a lot of people the problem is that they don't want this country to turn into Tescoland 
If Tesco become so big that they wipe out the competition then they will be able to do pretty much whatever they want and no-one will be able to stop them.
They have also acquired their monopoly using some fairly unethical methods which a lot of people are opposed to.
I don't shop in Tesco anymore (actually, we don't have one here anyway so there's no moral dilemma

).