Instead of making FPs and DCs a default type of AI, let's make these into midgame events.
Purification War
In the midgame there is a chance that an empire will become a FP. Militant and hierarchical empires get a bonus to this chance. The empire must be fanatical xenophobic. A player maybe become a FP through an event chain. This is different from a merely aggressive empire because FP's have special mechanics regarding purging.
-Every pop purged, space monster killed, species genocided, enclave destroyed, and empire erased from history. FPs will get unity, influence, happiness to xenophobes, and ethics convergence.
-Double influence from rivalries. Double number of rivalries.
There is a timer on the last pop purged. If the timer runs out, the FP reverts to a normal empire.
Liberation Wars
Similarly, there is a chance in the midgame that an empire will become a DC. Militant and xenophilic empires get a bonus to the chance. The empire must be egalitarian. A player can become a DC through an event chain. Unlike FP's multiple empires will become DC's, and they will ban together in a federation. The federation will have a special name like "Alliance of Democracies" or "Confederacy Against Atrocities". All members of the federation get a special CB to force non-democracies to become democracies and join their federation as a non-voting member.
-Every non-democracy "liberated" grants unity, influence, happiness to egalitarians, and ethics convergence to all federation members.
-Bonus if the liberated empire is an autocracy, had slavery, committed atrocities, or attacked primitives.
There is a timer on the last empire liberated. If the timer runs out, the DCs revert to normal empires and there is a high chance of them leaving the federation.
I think you can also see how there would be similar events for other ethics as well. The events should focus on how a civilization's galactic view is shaped by contact with aliens. There is no reason for an empire to be fanatical purifiers if they've never met aliens before, or to believe that democracy must be spread through wars is they implicitly think the stars are empty. This should come later as a result of experience with aliens.
Purification War
In the midgame there is a chance that an empire will become a FP. Militant and hierarchical empires get a bonus to this chance. The empire must be fanatical xenophobic. A player maybe become a FP through an event chain. This is different from a merely aggressive empire because FP's have special mechanics regarding purging.
-Every pop purged, space monster killed, species genocided, enclave destroyed, and empire erased from history. FPs will get unity, influence, happiness to xenophobes, and ethics convergence.
-Double influence from rivalries. Double number of rivalries.
There is a timer on the last pop purged. If the timer runs out, the FP reverts to a normal empire.
Liberation Wars
Similarly, there is a chance in the midgame that an empire will become a DC. Militant and xenophilic empires get a bonus to the chance. The empire must be egalitarian. A player can become a DC through an event chain. Unlike FP's multiple empires will become DC's, and they will ban together in a federation. The federation will have a special name like "Alliance of Democracies" or "Confederacy Against Atrocities". All members of the federation get a special CB to force non-democracies to become democracies and join their federation as a non-voting member.
-Every non-democracy "liberated" grants unity, influence, happiness to egalitarians, and ethics convergence to all federation members.
-Bonus if the liberated empire is an autocracy, had slavery, committed atrocities, or attacked primitives.
There is a timer on the last empire liberated. If the timer runs out, the DCs revert to normal empires and there is a high chance of them leaving the federation.
I think you can also see how there would be similar events for other ethics as well. The events should focus on how a civilization's galactic view is shaped by contact with aliens. There is no reason for an empire to be fanatical purifiers if they've never met aliens before, or to believe that democracy must be spread through wars is they implicitly think the stars are empty. This should come later as a result of experience with aliens.