Ethics are fanatic egalitarian and xenophile, game goal is to convert everyone to the same ethics and unite them into a big loving federation. The other civics are in the moment meritocracy and functional architecture. In the end I could leave it as it is, I just hate waste
In that case Parliamentary Democracy is probably best. You can use the influence to fund galactic community resolutions to shape the galaxy's ethics. The Greater Good resolution tree can outlaw slavery and compel the AI to adopt Egalitarian living standards (Social Welfare and above), which have the impact of encouraging Egalitarian ethics.
Meritocracy and Functional Architecture are good at all times, but if you're not trying to min-max and are trying to maximize your galactic federation size, consider replacing them with Free Haven and Diplomatic Corps to lean into your playstyle a bit more.
Diplomatic Corps is great for getting your Federation cohesion back up and running with larger groups. While Ethics alignment should help, you'll still take huge hits to cohesion for each new member added.
Free haven is a rarely-used and often-overlooked mid-game Federation perk only for Xenophiles. It increases Immigration Growth by 15%, and Immigration pull by 50%. In a Federation with Migration Pacts enabled for free, this means that- compared to the AI- you'll steal pop growth from your fellow Federation mates, even as they will naturally grow more aliens and thus become more Xenophile.
In the future, though, if you ever really want a 'whole galaxy united in ethics' build, go Spiritualist. Spiritualist has the most and highest potential modifiers for ethics shift chance that you can both get for yourself, and enforce on your neighbors. Between being a Spiritualist overlord, having a trade/defense pact/federation with a spiritualist, having a migration pact with a spiritualist, having psionic pops in the empire, and the Divinity of Life Galactic Community tree, you can swamp the galaxy with Spiritualist attraction modifiers. Add to that Temples (for planetary ethics buff) and- if Mega Corp- Temples of Prosperity to boost on other planets, and it can get extremely self-reinforcing real quick.
Do it with a Highly Adaptive Plantoid Species with Budding and Deviants, and you can even get your pops to be the dominant species in the galaxy in most empires by the end. The Adaptive will make them the first-pick to grow on planets from migration pacts, the Budding will pre-empt robot assembly, and Deviants will break down initial ethics until your galaxy of spiritualist modifiers overwhelms.
