If they are truly on a vacation and there is no chance of them being called back to duty at a moment's notice then OK they should be allowed to drink.
But if they could be called back at a moment's notice then they shouldn't be allowed to drink during that time.
Same for doctors or nurses who may be called back to duty at a moment's notice.
It is their right to drink but they should know if their performance is compromised they would get demoted. Drinking can be the same as not keeping their body conditioned and tip top shape, if they're not going the gym to improve their physical prowess that could be the same as going to drink. Alcohol is good for socializing but it's definitely not something that will help you in field work.
Yes Secret Service agents should be allowed to drink when they are off duty, but only when they are not subject to involuntary recall to duty. Agents who are working the Presidental detail, either as members of the advance party or trip staff, are subject to involuntary recall and should not be allow to drink while in that status.
The Secret Service should be free to enjoy themselves when not on duty. Granted it would not be advisable for any of them to over consume alcohol, that would be subject for termination. Even though their off duty is most likely still an "on call" position, they should be allowed to have some free time to themselves and partake in legal activities.
If an agent is on vacation they should be allowed to drink. But if they are going to working or could be called upon to work within 48 hours they should not. Drinking and it's after affects dulls the senses and critical thinking skills. Even when on an advance team, they need to be professional and sharp.
No, I do not think Secret Service agents should be allowed to drink when they are off duty. These men have a great deal of responsibility. They need to remain professional at all times, including when they are off duty. They should never put themselves in a position that would bring shame to their group.
No, secret service agents should not be allowed to drink when they are off duty. There may come a time when disaster strikes the nation without warning. In this case, agents would be called into duty no matter what the day or time is in order to protect the president. If agents drink off duty and disaster strikes, we cannot expect drunk agents to protect the president.