False, a women wearing pants would also be treated the same way. The thing is that the association of pants with significantly more men than women is similar to the situation with a back pack. Why not use the example of make up then.

NO MAKE UP ALLOWED IN MY STORES! If you steal something the makeup could help concealing your identity to the surveillance cameras! Of course men could wear make up too and be subject to the exact same treatment as the women who are not all allowed into the store but the rule clearly effects one gender more than the other.