I think the Blairs have been mentioned because people (including me) feel cynical about a lot of the rich politicians who could make changes to tax laws if they wanted to, but they don't because the current tax loopholes benefit them as well as Starbucks and Amazon (and, no doubt, other businesses). I don't think the issue is a simple black and white one though; I suppose they do have to consider driving businesses out of Britain by 'adverse' tax laws.
I've never been in a position to evade taxes (legally or illegally), but if I found myself in a situation where legally evading paying some tax substantially increased my income, I'm not sure I could resist the temptation to take advantage of a law that was an ass! I speak as one who has always had to be careful with money. I would accept a change in the law that made it impossible to evade paying the tax, of course. However, that's just a hypothetical situation.
As it happens, I don't use Amazon much, though I have bought the occasional book using it, and I also don't use Starbucks much though again, I have drunk their coffee when in dire need of a caffeine fix on a long drive! I'm not going to go into guilt overdrive about it!!
It would be good if a boycott such as this had the desired effect but I won't hold my breath about that.
I did say I was cynical on this issue!