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.