Oh my God humans are nomadic long distance runners with multiple mates that roam great distances but we keep them in small cubicles, sterile apartments, and automobiles and only allow one spouse. How inhumane!
See things can be argued against any type of confinement. One could say keeping snakes period is cruel but we do and those who are responsible caregivers do so in all sorts of mediums. If you are against tubs (I am too) then don't use tubs but don't knock the people that do and keep healthy snakes.