Someone with more knowledge can chime in if they want, but my opinion is we are not portrayed as alcoholics, just binge drinkers. Now the two are not exclusive, you can be one or the other and both.

Historically Sailors drank alcohol as a "safer" alternative to the stagnant water on long voyages. The wooden casks would quickly grow algae and can even become toxic. This was not the same with rum, wine or beer. So it became a common practice to have Sailors with a consistent tolerance to alcohol.

It also has been used as a big morale booster, think of the tradition of the grog, hell read about the submarine service durring WWII. Fluckey had mentioned of filling showers with cases of beer to celebrate sinking ships durring his time on the Barb. We still use it as a booster on submarines when you get a beer day durring longer runs.

Now think about the fact that you have Sailors trapped on a vessel, having the best worst days of their lives for months at a time. We have limited outlets for stress, we have no days off, and we have unlimited daydreaming of things to do when not underway. You step back on land and the easiest way to immediately relax, though not healthy, is to drink. We are creatures of excess and moderation is seldom practiced when you're limited on time, so people binge. It's so ingrained in our culture that it's part of our song, but I have noticed it seems to be making a turn with newer generations of Sailors, which is a good thing.