Modern Liberal democracy holds the ideal that we should maximize the liberty of individual citizens while minimizing harms to both individual citizens and the community of citizens as a whole. It's a system that technically tries to be preferential to everyone at the expense of nothing and no one. Needless to say no one actually knows how to do that, but the intuition since the 17th century has been that this can best be accomplished by distributing political power as equally as possible among the entire citizenry. 'One person, one vote' is a slogan that comes from that ideal: it indicates that every person has an equal say in any decision handled by simple voting, and that every person has a voice in the government they are citizens of, no matter how small that individual voice might be.
In practice, every political system is encased within a socioeconomic structure with built-in inequalities, and these non-political inequalities always bleed over into the political system, creating implicit systemic preferences. Politics skews heavily towards the wealthy and the famous — socialites, successful executives, military leaders, the occasional actor — and there is perennial political/legal conflict over whether that implicit entitlement should be ignored or opposed. Further, there is a near constant push-back by people who do not accept the democratic ideal, and wish to establish an explicitly preferential system in favor of those (i.e., themselves) whom they feel are deserving. In the usual case, these preferential groups work against each other, vying in competition, and unintentionally hold something like the democratic ideal through dynamic tension, but occasionally one garners enough power to rise to the top like... err, not like cream, as it were... and become a threat to the system as a whole.
Democracy is messy, convoluted, and contentious, but nowhere near as fragile as it might appear on the surface. Its ideal is very hard to kill, even if its institutions come under threat.