If all were relative, even relativity would have to be relative, for that assertion to be consistent. And then, relativity would crumble, and the same longing for some truth would remain in the end. After all, theories that purport to hold that every possible act and ommission is fair and legitimate ends up endorsing acts against which many consciences object, and thus become complicit and reject those who opposse the unfairness, becoming totalitarian in the end. Maybe this is why Dostoievski said, in the lips of the characters of the Brothers Karamazov, that those who deny the existence of God deny the possibility of limits and duties, and may endorse thoughts that injure others. Not only denying God, but denying the possibility of a truth, can do this. After all, if I do not perceive the red color, I do not deny that my perception is different from that of those who can see that color, but the differences in perception do not change the fact that something is red.
Furthermore, relativity may be a self-fulfilling prophecy and, like conspiration theories well criticized in Foucault's Pendulum by Umberto Eco, may make those who endorse it behave as if that relativity were a fact, in which case they may fail to perceive a truth and, ironically, make them hold that relativity is a truth in itself, crumbling relativity in the process.
