Before, I dont mind it why we are using paper as money. But as a citizen, we have to obey what does the law says and our countries has the same law with it. As they declare something like paper/cash as money, it will turn out that way.
I just realized it lately, yeah why we have to use paper as money if our ancestors successfully live through trading "barter", exchanging of goods to goods/services vice versa.
Your comment explains why we are still sticking with paper money. Yes, being a responsible citizen we do not have any other options expect adopting paper money of our governments. But, after some enlightenment like bitcoin, I believe anyone will come forward to start using new type of currency for sure.