The only cons I find in the cashless is you need the internet and the entire world is still not connected totally with it.( even electricity is one of the major problems)
Non-cash transaction are currently very popular with the public just because it make it easier for them. People no longer need to carry a lot of money in their pocket just to shop at supermarket or the like because they only need to use an ATM. It has become a modern payment system.
But when it come to bitcoin, I think it will still be difficult to implement in countries where the status of using bitcoin as a legal means of payment has not been legalized. Although bitcoin is much better than digital currency, its illegal status as a currency in some countries will hinder its adoption.
Non-cash transaction is no doubt good. I remember in my childhood there was an option to send money through the post using money order. This kind of procedure become simplified by NEFT, and now by UPI. I won't like to compare between fiat and crypto because they are so different. In crypto people are really independent of their own money. But as per the current situation people will rarely choose BTC, because of price volatility, even if it is legal.