It's shaming them for legal, but unethical behavior.
There's a lot of behavior that falls into the area of "legal, but shitty." Large corporations gaming the system to avoid paying taxes falls into that.
Don't kid yourself that we can ever totally eliminate this kind of thing. It's a moving goalpost. You pass laws to stop one kind of thing, their highly paid attorneys and accountants will find something else. It's cheaper for them to pay smart people really well to find loopholes than it is for them to pay their legitimate tax rates.
If we all behaved the way corporations do -- sticking only to the letter of the law, and exploiting every other opportunity to better ourselves at the expense of everyone else around us -- the world would be a really awful place.
We have to point out this behavior and shame the corporations, because negative public opinion possibly affecting their bottom line is the only thing they will respond to.