All companies who have shareholders are obliged to do everything they can to maximise profits. It is not optional. If you wanted to avoid spending money with companies who act unethically, you'd be foraging for food in the woods to take back to your cave, wearing animal skins which you have hunted for with tools you have crafted yourself out of tree branches and flint...
You are cutting your nose off to spite your face because you refuse to use a particular vendor, irrespective of the benefits, over a largely irrelevant point.
I should point out that I in no way support the philosophy of corporations not paying tax, but as stated, the blame lies with the government, not the organisations themselves. I am simply a realist.
Also remember, the customer isn't King! The customer is an integral part of the commercial model which also relies on manufacturers, distributors and vendors. Removal of one, damages all of the rest equally.