I guess sex on the first date is fine, but I wouldn't use it as a barometer to pursue a relationship other than a sex-based one. From my experience, sex on the first date has led to either: 1. unsuccessful attempts at a relationship (having realized over time that the two of you are not compatible outside of sex) or 2. awful sexual encounters (which primarily occurs through meeting someone from the internet for the first time– mystery grab bag sex, lol).