It prevents a key economic activity: borrowing money. I'll let you put together why deflation kills incentives to loan money, hence making it impossible for people to borrow.
Once you've done that, please explain to me how there were loans made over the last 400 years in light of the fact that only the last 80 years has had reliable consistent inflation.
If you live in a time of high barriers to borrowing money, you will live in a time of vastly decreased social mobility. You know, kind of like the time prior to the last 80 years. That wonderful age you gold-standard lovers wish you lived in.
Inflation is worse for lenders than deflation. Each dollar they get back is worth less when it is returned, not more.
Borrowers love inflation. If there was great deflation, it gets quite painful to pay back loans. The lender is quite happy about it though.
I think I read, though, that both severe deflation and inflation push up rates. If deflation is severe, it can push many borrowers into bankruptcy, making lending more risky.
The real story is more complicated since I have ignored money demand.
Note that I have not said Bitcoin will become a 'real' currency. There are real problems, Im just saying that your argument is wrong.
bitcoin's inherent deflation is not by money destruction nor increases in production, thus these arguments are not relevant, although true within its own context. since bitcoin, like gold, has a finite quantity, deflation is mostly due to demand, which you have chosen to ignore in your argument.
What you have just proposed is an increase in the cost of starting a new business, no matter how good an idea is. Just because the banks are bad at determining who can and can't pay back a loan doesn' mean those who CAN should pay a tax.