You might be right about human nature, but I don’t think that the current state of lemmy is a good argument in that direction. Since there isn’t a way to aggregate multiple communities together, network effects drive users towards centrilization. It’d be interesting to see what happens if cross-instance community aggregation becomes possible.
And they didn’t just start serving ads, they started serving ads like the HeGetsUs campaign that were so poorly targeted that the community they’d built absolutely hated them.