An addiction to the dopamine rush from ALMOST winning is very much a behavioral bug that some humans have that makes them very susceptible to gambling addiction.
We don't get to decide individually, but we as a society get to decide, via our (hopefully representative) governments.
This kind of argument is not particularly interesting; the entire point of a discussion board is for everyone to post and discuss their opinions, which will naturally differ sometimes. Asking what amounts to, "why are you allowed to have that opinion?" is pretty pointless.
We can endlessly debate morality, ethics and all that regarding lots of things, but in my humble opinion gambling could be reduced to:
"Would people still engage in those games of chance if there was no monetary aspect to it?"
And then how many of those people who would still engage with them are "notorious" gamblers on whom those games had a clear negative impact (in most people's eyes).
Let's demonstrate that by just jumping to the end of this reasoning -- severely mentally retarded adults -- can they consent to sex? Why or why not?