how does Monero help to prevent governments from taxing bitcoin? 

 I'm not following, if you use a centralised exchange *which is what we are discussing here) Monero would be taxed too. 

 Because decentralised exchanges are sadly not ready for large amounts of money.

I'm not defending centralisation, I hope we move towards that way.

My point here is that bitcoin can also be used in decentralised exchanges, you don't need monero. 

 I've tried to DM you but it doesn't seem to work.

I'd love to help testing it.