If I create a currency, and use it regularly in my household between residents in my household, and I agree to let you stay in my household, and let you use my currency, and i let you own stuff in my household at my discretion, and I charge you a fee based on transactions you engage in using my currency in my household, is that theft?
That's basically what governments do.
What if bitcoin charged you a fee for engaging in transactions using bitcoins? Is that theft?
Depends; was the household fee clearly stated when I first moved in, or was it created after? And may I opt out if I decide I no longer want to use said currency or the benefits it entails?
What was stated when you moved in was that the rules can change. Take it or leave it. If you were born in my household, play by my rules or leave. Clear enough?