Ilan, a loyal MR reader, asks when a restaurant decides to make its bathrooms "customer only." I see a few factors:
1. Fear of drug use or illegal drug dealings in the bathroom; the importance of this factor seems to have declined over time.
2. The belief that some people will buy a drink just for bathroom rights. We did this in Brooklyn on Saturday and it was worth it.
3. The desire that only paying customers shape the ambience of a restaurant; this is important in areas with gangs.
On the other side of the equation is fear of Jack Henry Abbott, the realization that any restriction is not fully enforceable, the desire to cultivate good will among potential customers, and giving the visitors a chance to look at the food and atmosphere.
Overall I’ve found that restaurant restrooms are more available to non-customers than ever before and I attribute this to the aging of America and the greater likelihood of a sharply declining marginal cost curve. In other words, at least until this year raw materials expenses weren’t so important so the profit value of an extra customer was pretty high and restaurants would do a lot to cultivate good will. In general rising commodity prices mean decreasing margins (retail prices don’t rise by full offset) and thus adjustment on other margins, such as portion size and service quality. The bathroom isn’t as clean as it used to be either.