The Night's Watch is NOT a Democracy. Elections don't necessarily equals Democracy.
The presence of an elective system is not a synonym to democracy, it merely means that the leader(s) (not ruler(s)) of that political subject are chosen with a vote.
In real world, a democracy is a system of government where the power is held and exercised by the people, and can be either:
* direct, when the whole population actively and directly participate in the political life, by collectively debate and decide about all the matters;
* representative, when the population elect representative officials that carry the responsibility of the government, whose powers are usually balanced by apposite measures, and where it is applied the rule of law: so it is law that governs the subject and not the individual decisions of the elected officials. Officials are also elected for a given amount of time and do not govern for life.
We have several examples in our own history of political systems that used an elective system but were not democracies:
* in medieval and renaissance Italy, we had Maritime Republics that generally speaking had elected rulers and parliaments: in example, Venice was ruled by a <PERSON> and by <PERSON>*, but the former was de facto* a prince that governed for life, while access to the latter was hereditary and reserved to sanctioned patrician families.
* another example is the ecclesiastical government of the Papacy, whose leader is elected (only by a restricted number of individuals) but hold absolute power, and where all other ranks and positions are appointed from above, by the Pope itself if high in the hierarchy.
* a further example of a form of government whose leaders are elected but also exercise almost always absolute power are the monastic military orders like the Hospitaliers or the Teutonic Knights.
These kind of governments used elections, but were aristocracies, oligarchies if not even absolutisms, not democracies.
Back to Westeros, we know that the Commander of <PERSON> was elected, but otherwise governs as an absolute ruler: other ranks and positions are appointed by him (like the commanders of the forts), not elected as well, and he, like his title suggests, commands and gives orders to other Brothers; he was elected to rule for the rest of his life, and there is not a rule of law under which the law itself the is supreme ruler (granted, there is the Oath, but it basically was just a rule to not desert, to celibate and to obey to your superiors).
The powers of the Commander is not held in check by balancing measures, disobeying to him is treason, and as we know by at least two examples, the only way to disagree with him is to kill him.
This is really far from being a democracy.
The form of government from our history most similar to the Night's Watch was an aforementioned Monastic Military Order, where the religious and spiritual connotations are substituted by a supreme sense of duty. Even the celibate, the apprenticeship and the subsequent Oath, the strict hierarchical organization are common points. 274