Gambling will remain even without bitcoin and if gambling was not introduced then you are right with it bitcoin industry is not going to boom because one of its biggest contributor for its adoption and demand are the gambling sites and you forget to thank also those addicted gamblers because they are the once who is making the whole gambling industry alive. But if gambling is not introduced to the whole nation, then we will have our own addiction in other things.
Granting that gambling was introduced and invented, then bitcoin will still be use for online transactions - it just happened that gambling industry took the wave out of bitcoin but we have to realize as well that bitcoin is also being used in other financial transactions online.