* If I many ask what is the major reason while some countries ruling class ban bitcoin transaction?
They couldn't stop it and they couldn't track it easily.
* What is the negative effects using crypto as currency?
I don't really see any negative effect on it unless it would get you too addicted and could destroy your life like risking it all in crypto and couldn't handle it properly.
* what harm does bitcoin contributes a country that can lead to ban?
Illegal activities like money laundering which is pretty famous and it is the reason why government is against it,
Also being used as currency in black market for drugs and all sorts of stuff.