USD is the dirtiest fiat there is because it's backed by blood at a global scale.
As for moral purity, it's no secret that a significant (albeit unknowable) portion of Bitcoin's current value comes from illegal transactions concerning everything from human trafficking to drug sales to organized crime rackets. The ability to obfuscate financial transactions is part of its intrinsic value, so anyone with an interest in doing so will be attracted to it. Plus if Bitcoin were to somehow grow large enough to even consider replacing the dollar, all the blood behind the dollar would simply shift to Bitcoin in some (albeit likely different) manner. Someone has to enforce monetary policy and financial laws, a chaotic, decentralized enforcement would arguably be even worse than centralized fiat enforcement.
There's no way forward financially without some blood on your hands at some stage. So for my money I'm going to build my financial house on solid ground. I'm all for making the system more just and less bloody, but IMO Bitcoin isn't it. In the meantime we've all got to play the hand we're dealt, the only other option is to be a martyr, and while they might get some occasional press and lip service, martyrs typically don't accomplish much.
No. Internal trade is balanced with target2.
The EU came the closest, but no one outside of Europe has wanted Euros since the Greek economic crisis. Hell a large chunk of internal European trade is still done in dollars on the back-end.
On the stick side, under Obama the US stepped up the various mechanisms such that we can cut off trade denominated in dollars on a whim to anyone we want, that's part of how sanctions work. If we (the US) decides we don't want a country to be able to trade internationally, we just cut them off from converting into dollars at the exchanges. There are no economically viable ways around this at present. Just ask Iran.
Bitcoin however, will collapse the moment enough of the crowd loses the faith. It'll go on for a while because it's the new hotness, and some people will get lucky and rich, but at the end of the day it's an ultimately worthless commodity (unless you're trying to avoid government regulation over financial transfers) that exists as long as world governments allow it to exist.
Sure, if theoretically some critical mass of the population all collectively decided Bitcoin was the future it would be, but right now we can't get a critical mass of US citizens to wear masks during a pandemic that's killed hundreds of thousands. So I wouldn't hold out too much hope for pan-Bitcoinism.