Duct tape is a brilliant solution! The flight crew should get raises and be cheered as heroes. Of course, physically restraining unruly passengers doesn’t stop them from being verbally abusive and annoying to other passenger unless you cover their mouths with duct tape as well. If you use the toughest and most adhesive duct tape, it really hurts when it is taken off. I think the FARs already give flight crews the authority to do whatever they need to do to deal with dangerous passengers. The airlines are worried about lawsuits and loss of profits but they shouldn’t be. Unruly passengers and the risk of catching COVID have far more of an effect on their revenue than flight crews doing a service for the rest of the passengers and crew. Maybe some legislation and regulation changes are needed to make sure that the airlines and flight crews cannot be sued or prosecuted if they restrain an unruly passenger. Just drinking isn’t necessarily a problem as long as you don’t become an ugly drunk.