If one piece of cake is good, then why wouldn't two pieces be better? Makes sense.
So why doesn't it apply to alcohol the same way?
The first thing you have to consider is that alcohol, although technically a depressant, acts like a stimulant in low quantities. This is why when a person first starts drinking they will get a little more energy, feel warm, and report having that 'good buzz'. However, after a couple of drinks, alcohol starts to act like a depressant, meaning you start to slow down, lose energy, slur your words, lose coordination, etc.
After you get past a BAC of about a .05 (calculate your own BAC), those depressant effects kick in. Alcohol's effects look more like this:
The time spent with that 'good buzz' is called your staying in your green zone, this is the BAC range where you're likely to avoid the negative consequences of alcohol, such as memory loss, vomiting, or a hangover the next day. Check out the Green Zone link of Alcohol and Drugs 101 for tips and advice on how to stay in your green zone.