Nothing prevents a parliamentary democracy from going totalitarian. Nothing about parliaments guarantee free speech or right of dissent.
OK, make an absolute monarchy. Have it go on 7+ uncontested successions. Then the son is super smart but too lazy to actually rule, so he hires people to "run the country and think about it." No one dares removing the monarchy since they are ruling in his name and the monarchy has too much legitimacy. The first group of rulers once the lazy prince becomes king is his friends. As power hungry people come into court, they all try to win his favor. The de facto rulers ends up being a hodge-podge of people who can't end the charade.