I have a slightly different view on this, I disagree with some companies' use of it, but my young brother DID get a paid job at the end of it & whilst doing it felt he had a purpose for the first time in ages.
Also, I think that blanket boycotts & advertising bans are disingenuous. The equivalent if you like of 'leave the bastard'.
Presumably we should all also stop donating to the charities involved too? Would it not be less passive aggressive & perhaps more effective to write to the company (charity) in question setting out your concerns?
Boycotts have little or no effect unless a significant enough section of the population participate. In reality it is highly unlikely that a company like Tesco will be significantly affected.