//The discussion to be had is whether it's unnecessary and dangerous//
Why is it either?
Unless you subscribe to the Luddite school of progress, any facilities which make life easier (such as doing away with the need for cash) must be beneficial. To ask whether it's "necessary" is a little strange. Nothing like that is necessary. We can all manage without credit cards, debit cards, cheques, internet banking, and everything else to do with our finances that makes life easier. But life would be so much more troublesome.