No, I don't think the holidays make people anymore vulnerable than going away on vacation. Some people have the mindset that holidays and vacations are all about living like there is no tomorrow. No matter how you slice it everything we do is by (choice). If someone decides they are not going to be "alone" they are taking a "proactive" stance when they step out for the night or invite someone over.
Vulnerable is generally defined as being defenseless, weak, susceptible, or helpless. One could hardly claim that as their excuse as they head out to a New Year's Eve party. Even those that "drink too much" more often than not do so intentionally looking for liquid courage to follow through on their goal of not ending the year alone.