Which leads us to the fundamental problem.
Inability to pay taxes means the whole economical system goes down.
No taxes = no economy. It's basic. A state, a government cannot function without taxes, they are essential for a countrys development.
And because you can't tax zerocoin, most probably governments will outlaw any legal transactions with zerocoins. So exchanges will not be able to trade these coins legally. They will still be used, but their value would be almost 0.
See my point? Which is also where bitcoin is heading if it can't be taxed. If bitcoin is to be universally adopted, it would have to be regulated.
Which kinda sucks. Don't get me wrong, I don't like the idea.
You bring up some valid points about taxes, however I think you overestimate the Governments control if this were to be implemented into Bitcoin. Also, many people feel that the Government wastes our tax dollars on unnecessary policies, this would enable us the people to take back financial control of our government, a truly democratic financial model. Simply make each person pay for what services they need or want. If they don't want protection from the police, they don't have to pay for it. If they don't want to fund a war across the ocean, they don't have to pay for it, etc.
The TOR network for example would be a prime place to have a ZeroCoin/Bitcoin exchange. Even though most tax system run on the honor system, the Government cannot tax you for an amount if they don't know how much it is or who owns it- ZeroCoin makes transactions completely anonymous. As long as the Bitcoin network is safe, then this idea could work if someone was to never exchange into FIAT and just buy things with their Bitcoins. I imagine there will be many many places that accept Bitcoins in about 10 years.