Bitcoin has all the advantages of digital cash and allows one to be in control of their money. Although involves taking security precautions, it's what makes it such a good currency for the future.
Yes the advantages of bitcoin makes it most suitable and flexible payment system for almost all the sectors.
The gambling and porn industries growth are few example, how bitcoin contributed to those sector's development.
Bitcoin will be the future currency and that is because you also see that there will be more people that is going to have some Bitcoin and that is nice.
But you dont know what is going to happen with Bitcoin and that is the problem.
There's even a worse problem than not knowing what is going to happen with Bitcoin.
Let's say bitcoin does indeed become really successful (as if it isn't successful now) in the future. I can see one problem and that's probably monopolism.
Since the coin cap is at 21 million, imagine if one individual or a party gets a hold of a majority of those supply. That party would then be able to manipulate the price and supply at his will.