Sadly, the right has completely hijacked the high ground in this debate. Or, more accurately, the finance industry has hijacked the right, who now does their bidding without asking any questions (as does most of the left). Off shoring could be fixed by penalizing those who off shore money, both financially and publicly (i.e. it needs to seem unpatriotic to not pay taxes). As Milton Friedman pointed out, if you want less of something, tax it; if you want more of something, don't tax it. There has to be a way to punish those who hide money with punitive taxes that make it less attractive to do so. As for the inheritance tax, unless and until we stop the right wing media machine from calling it the death tax, we'll get nowhere. The inheritance tax, or lack thereof, will doom us all in a couple generations when the Waltons' children's children's children are still our corporate overlords. I believe Piketty refers to the type of taxes we need as "confiscatory". That may be accurate, but it's a hard sell to people who currently believe they're already overtaxed (even though marginal rates are lower than any time since before WWII). His math works, but the current PR does not. As off putting as it sounds, I think that the moderate left would score a lot more political points if they focused on couching the debate in terms of civic responsibility, rather than poor vs. rich. That is, it may be better to try to convince rich people that instead of just giving their money to the "takers" that it's being used to support the society we all live in--that we need them. I don't know that this is strategically viable, but flattery works on narcissists. Maybe if those in the high marginal rates felt more like the gate keepers, and less like the victims, they'd be more willing to support progressive taxation.
Behold FATCA. I'd never heard of it, have you? Piketty mentions it after he goes on about offshore accounts and points out that it's the first thing in a long while to actually penalize shady offshoring, and that it has the teeth to actually change banking. Meanwhile, the right wing noise machine has been calling it the "death tax" since Grover Norquist was in short pants but it still exists. Believe it or not, I'm optimistic on this one.
I wouldn't have been able to mention FACTA by name, but I remember an NPR report from a couple years ago where they mentioned the IRS getting pretty short of patience with some Swiss banks for not being forthright about who their patrons are, because those patrons are now required to pay taxes on that money. If only they could do the same thing for corporations. All the big multinationals refuse to bring lots of capital to the US for fear of being taxed. There has to be a way to make it more painful not to do so. Another think Piketty points out is that this requires an international regulatory regime--one more thing that scares the sacs off of right wingers.
It doesn't, though, and he doesn't make that point. He makes that point that the quickest, simplest way to make things happen is an international regulatory body while in the same sentence observing that the political climate makes such an idea laughable on the face of it. And these are in a few flippant comments scattered throughout the book - while he spends a chapter or two pointing out that simply enforcing the existing regulations governing world trade would increase global GDP by 40%.