You know if its ever made illegal.
How would making it illegal to buy or sell bitcoins prevent it from happening? That approach hasn't worked too well with buying or selling drugs.
Not even a smart comparison. Drugs are addictive. No one has a
need for Bitcoins. Add to that, as long as fiat is easier and more practical to use, it will always dominate because people are lazy and will use what is most convenient. Bitcoins are anything but convenient and easy to use.