Democracy is a form of government, not an ideology. Just because +50% of an electorate thinks something is OK, doesn't make it so.
Let's be careful here, the point in favor of democracy is not that the majority knows best, but rather if that people are to be subject to laws, then those same people should have an equal share in determining what those laws are. IOW, the point of democracy is to give the people what they deserve, and no more.
With liberal democracies, I believe it's more about self-determination or fair representation than who knows best. The point is to prevent tyranny, including majority tyranny.
There can be no liberal democracy without the protection of human rights and the of law.