First, a slight clarification: while the main charge and the detonator were separated during transit and intended to be assembled on the plane, the explosive liquid itself was not a binary compound; it was live in the soft drink bottles.

It sounds like you're arguing that this regulation is not necessary any more because that particular plot was foiled. I find that line of reasoning odd, given that the 2006 attack was the last in a string of plots using liquid explosives to target airliners. The type of group which carried out attacks like this still exists, with similar goals.

Given that it's reasonably effective at deterring a technique which has actually been used (the Japan test run in the 90s) and which has been attempted multiple times, I think it's possibly the least objectionable regulation. It doesn't address all modes of attack (obviously), and it's very debatable whether the likelihood of attack makes the invasiveness of the countermeasure acceptable, but unlike body scanners it's at least effective at deterring the specific modality it's aimed at.