Money was invented as a medium for exchanging value:
you give me value, I give you money,
then you give someone money, and they give you value.
In this scheme, the person who ends up with more money is the one who has provided more value to others. Everything is clear and fair.
...until we begin to talk about USD

It would be much better to play for something else. For example, for points.
Cryptocurrency actually fits this quite well too. Especially coins that are given away in airdrops, or those that are easy to mine. Or, really, any coin that only pretends to have value.
So overall, it seems quite logical to me that the most popular board on Bitcointalk right now is the "gambling" section. The most obvious use case for cryptocurrency, wouldn't you agree?
Cryptocurrencies costs money. You can mine it, spending money to buy mining equipment, pay money for electricity bills, or you can pay fiat money to buy cryptocurrencies. So using cryptocurrencies for gambling is the same as using money.
For me there is no difference between cost of money and cryptocurrencies. I use money for betting i sell my cryptocurrencies for expenses.