those people who buy bitcoin just for the sake of gambling with it are also trying bitcoin as an investment, they are doing everything wrong though. but they use it as an investment nonetheless and think they can make profit with gambling that is why they try it.
Yes, gambling never will be a way to grow our bitcoin investments, those who are trying to have more amount of bitcoin through gambling will be ending up losing all their bitcoins.
But the good things, they are doing with bitcoin ecosystem must be they are buying for their own reason of gambling. Buying is always good for bitcoin system but buying for gambling is not good for any individual person.
As long as they can afford it and they are not addicted to gambling I dont see anything wrong, will they lose money in the long run? Its very likely since most players are long term losers but if that is the way they like to have fun then that is fine.