. . . can he decide that riding a motorcycle or skydiving are dangerous hobbies and fire people who do this on their weekends off?
Are you claiming that there's some inalienable right to motorcycle riding or skydiving? Of course there isn't. Not to say an employer wouldn't tolerate those things, but it is his or her own right to free association. Otherwise what would you suggest? Enslaving the boss to provide you a lifetime of paychecks because it would best suit you?
i am saying that there are limits to the amount of control that an employers has over his employees. your take is that the employer can force his employees to do, or not do, whatever he desires and that their only recourse is to quit.
that is recidulous on it's face. if you feel that an employer can ban his employees from riding motorcycles on their own time and that thei only recourse is to quit, then you are very badly mistaken.