Freedom is never absolute. You can respect other people's freedom to disagree with you, but not their freedom to kill you. You can choose to only stop them from the latter, but not the former.
Basically absolute freedom means less freedom overall because the strongest take over. Limiting freedom (eg you can't kill others) can mean more freedom overall as more of the population are able to exercise their (limited) freedoms.
Am I the only one to see an interesting parallel to "copyleft" (e.g, [L]GPL) licenses (and a refutation of the "It's evil, viral, anti-free!" objections to them) here?
Democracies can suicide. The Weimar Republic did (though notice that Hitler never actually won a popular majority vote).
This problem was exactly what the American Founders had in mind as they shaped their Constitution. They wanted to identify the ways a government could be turned against its own people, and create barriers against those attacks. The US doesn't trust majoritarian government, which is why it isn't exactly a democracy. Items like the Bill of Rights, and features like the separation of powers, are intended both to secure liberties and hamstring oppression.
(The Federalist Papers are a fascinating discussion of all this.)
But at the end of the day, constitutional features can only slow down an oppressive majority. If a majority wants to dominate a minority, eventually they are going to find a way. The only real security for freedom, over long term, is to raise up a people that think and feel and act in those ways that are consistent with freedom.