Yeah but gbl has like 20 times the character of ethanol. Forgetting for a second that gbl is only a solvent until you put it your body where it rapidly get's converted to GHB. The problem with alcohol is not that its a solvent, you can get complex solvent too - well slightly more complex in anycase. No the point is that ethanol is so simple that it literally will bind with any receptor it comes across. This is the exact reason why we have to consume 80 grams of it (four pints of stella) just to get an moderate effect (there are nuances to this argument that we can go down if we like). The bottom line is that ethanol is so simple, symmetrical and lacking in distinguishing features that it will bind to just about any receptor it comes across. This is why alcohol binds to gaba, NMDA, dopamine, serotonin, noradrenaline, as well as all the opiate receptors too. It's complicated though as it does not all of them at lower doses. Some of these systems, notably the NMDA receptor (of Ketamine fame) and the opiod family only kick in at higher doses.