They were already arresting the people who tried to sneak antrax on to planes. The limit on bottle size was in direct response to a tactic that was attempted to subvert the existing security by sneaking component chemicals that were not by themselves dangerous onto planes in sufficient amounts, where they could be combined into a weaponized form.
In other words, you can't take your shampoo bottle into the cabin of a plane because someone figured out how to use shampoo bottles to blow planes up...not because they didn't want people washing their hair in airplane lavatories.