The basic purpose of the TSA is to prevent a collapse of the air travel market, and now it seems that a few related business interests are also part of that picture. What is or is not allowed through the checkpoints is as much determined by what the public is afraid of as by what will work well for airport businesses and airlines. The shoe rule is slowly but surely going away (it does not apply to anyone who participates in the various pre-screening programs that have been developed; I am guessing it will be gone in general a few years from now), but the equally pointless liquid rule remains in place for everyone. The only difference is that one of those rules boosts sales for airport businesses while the other only makes the lines to get through the checkpoints longer and discourages flying. The proposal to have all laptops go into checked bags was killed almost as soon as it was thought up, even though there was some legitimate concern about attacks strategies involving laptops (it seems to be more realistic than the liquids plot), simply because airlines said it would have too negative an impact on their ticket sales (especially for business class seats, which are the most profitable per square foot of cabin floor space).