Micro payments won't be a subject to mental transaction costs once the adoption reaches a significant level when people start viewing it as the money they can use any way.

Currently, I agree it does have a bit of mental transaction cost. But it goes away as soon as you find people willing to transact in it. Stacker News is a prime example of this. Here almost everyone zaps or be zapped for good work. Because everyone is doing it, it feels very normal.