General thoughts, not list of "useless" civics:
Pacifism
Folks have pretty much nailed how useful Pacifism is. One of the main hurdle cited (having to spread religion) in a way makes OR more important as a predecessor potentially. Maybe still not worth the high cost.
Serfdom
Agree on most of what's been said, especially
@crullerdonut's breakdown of the K-mod revamp. One thing that makes it so interesting is simply that it offers something quite different than the other 2 main Labor civics. The 3 do very different things, and that is a good thing. To make it better, some have suggested Serfdom could come earlier, with say Monarchy, since the worker bonus is less relevant over time. But since the
bonus is pretty decent, I'd love to see the benefit split up, where the
bonus still comes with Feudalism, but the base civic (now: worker bonus & -
penalty on Towns) comes with Monarchy. Perhaps some other tweaks would need to be made (Monarchy more expensive, etc.), but at least then the civic would be available right around the similar time as Caste at least. And also it's Low Upkeep versus Medium.
It'd also seem to make more sense historically, I'd say. I know that matters less to many, and I'd agree gameplay is crucial. But Serfdom has been around since ancient times in multiple cultures. Pairing it with Monarchy models that well, and Feudalism can still represent a more developed Serfdom of say Middle Age Europe & elsewhere.
Slavery
How overpowered this is. Remember in Vanilla when it was Low Upkeep? Yikes. Since most folks turn off Random Events for understandable reasons, the main nerf of Slave Revolts, is done away with. The Medium Upkeep in BTS, by itself, does little to keep if from being overpowered.
Emancipation
I'm surprised hardly anyone has mentioned this one as near useless! Especially in comparison to Slavery, Caste, and also K-mod Serfdom. It's just poor construction. Again, like Serfdom, its main positive bonus - faster cottage growth - is inherently nerfed by its late timing (and is of course overly-specific). While annoying, I actually do like the
dynamic that builds over time as more civs adopt it. The relativity of it is a unique dynamic. What makes its annoyingness so pernicious, is again that it offers little positive benefit.
I think one simple change, though small, would be to make it No Upkeep. At least then you pocket some $. And it would offer at least some benefit in comparison to the other Labor civics, a full 2-step upkeep reduction compared to Slavery & Caste. Not saying it'd be on net better, but the bonus would apply regardless of how many Cottages you're working.
And that'd make sense, realistically: Slavery, Caste, and Serfdom are all somewhat intensive systems of organization. Emancipation isn't even a system - it's an event, basically. What does the upkeep even refer to? Labor laws? Those are later additions to economies, which could be reflected by some kind of small bonuses to Emancipation from later techs / civics. Not sure how feasible it'd be to split features of a civic between techs, but if we're just spitballing.
Mercantilism & Free Market
These 2 seem to make me scratch my head the most, though not that urgently. With Medium Upkeep, Mercanitlism seems often tough to justify even with +3
from Rep. Especially since Low Upkeep Free Market is around the corner. I'm not sure how Mercantilism could be improved? Defensive bonus against Espionage? K-mod flipped their Upkeeps, and while that balances them a bit, I find it to be less realistic, while often negating Free Market's
bonus by its new upkeep cost. So then we wait til Corporations to really cash in? I don't like that. In that case, why not just stay in Decentralization? Which I just find a low-key frustrating dynamic. Another bonus to FM could be added, but to me the most logical step is to keep it Low Upkeep, as a minimalist type civic.
Environmentalism
Don't usually use this one, but I like it for having some very clear bonuses. One tweak I think that would offer something different would be a Diplomatic bonus while running it, to model increased international respect. The bonus could be gradual just like other diplo bonuses, and capped of course (+2 or +3?). That way it can't be abused last minute. But it would still have some unique utility for Diplomatic victories, along with maintaining trade routes, preventing late wars, etc.