Yeah, that is true, but I think its a big jump from potential to direct correlation. I mean working out may increase my testosterone, which may increase my aggressive behavior, which may increase the potential I attack my wife, but that does not mean I should not be able to work out.
If we were able to make a direct correlation such as every time I smoke pcp there is an almost 100% chance I assault someone, then I would accept that being illegal.
Driving drunk is another example. 9/10 driving drunk doesn't do harm to anyone, but it clearly increases the likelihood that you might.
I don't think we should make driving drunk illegal, because clearly the majority of times you do it, you don't do anything but drive home. My solution to this problem would be to drastically increase mandatory prison sentences for crimes/injury inflicted on another person, while eliminating victimless crimes entirely.
In the instance of drunk driving as an example. It would be perfectly legal to do it, but as soon as you hurt someone else, 25 years in jail. Same goes for driving recklessly, or anything that is known to increase the likelihood of serious negative impact on someone else.