re: Our ancestors were douchebags,so why do we admire them?

Our ancestors inherited slavery, etc and abolished them. While I have no doubt that you would have single-handedly destroyed the institution of slavery, in actual fact it was the work of lots of good thinking and brave acting on the part of many people you now casually deride.

You're basically standing on a huge rock, proclaiming how great you are for the wondrous view you command, and then pissing on the rock for having a view 6' lower than yours.