I think it's not illegal and legal because there are no rules about it.
I believe that depends on the current status of bitcoin and gambling separately in your State and Country. If you are allowed to gamble then you are not doing anything wrong, bitcoins just make gambling easier and there's nothing new with bitcoin gambling. I mean the casino remain same like sports betting or roulette and slot machine. Everything is same just the currency ( more correctly I should say Asset ) changed.
A responsible gamble also has to know the regulation of its country, when bitcoin gambling or crypto gambling is illegal then we should not try because we will all ended up cashing our bitcoins to fiat and that time we will be trace. So far, the crypto gambling is getting more popular so IMO it's not yet fully regulated and we gamblers have the freedom to do whatever we want with our crypto currencies in gambling.