You neglected to include a good argument in favor of slavery.
Some people aren't intelligent enough/don't have high enough time preferences to function in modern society. Thus you either need to have them under the control of a master, or you wind up having to put them on the public dole and institutionalize the many of them anyway.
True, however, the civil rights movement did.
For instance, suppose my cause is to prevent the growth of a hole in the ozone layer. I tell people they must stop using CFCs.
Well, that raises issues about just how serious a threat was the "hole in the ozone layer", and how much if anything it had to do with CFCs.
Stop hyper-focusing on individual words to try to score debating points when the intent behind their use is clear from the context, everybody on LessWrong.
There were good arguments for all of those things when they were still in use. There are no good Arguments today for favoring Aristotelian physics over Newtonian physics, Ptolemaic over Copernican, or the phlogiston theory over the oxygen theory, where an Argument means a complete consideration of the evidence and the individual arguments.
I'm not trying to score debating points. I have a serious point, namely that chances are you don't actually know most of the arguments involved, either here or in the political debate. Instead you rely on appeals to authority. This raises the question of how reliable are the authorities. Probably reasonable reliable in the case of physics, rather less so in the case of political issues.
Slavery, suffrage, Christianity or Prohibition aren't right or wrong in some objective non-moral sense. Arguments for or against such things are inevitably about convincing people, not about some objective truth.
Well three of those four things are essentially government/societal policies, and one can argue about what the consequnces of adopting or not adopting those policies are.
Let's test your idea that "There are no good arguments for X" is simply how having a successful social taboo against X feels from inside:
"There are no good arguments for the phlogiston theory of chemistry" is simply how having a successful social taboo against the phlogiston theory of chemistry feels from inside.
"There are no good arguments for Ptolemaic astronomy" is simply how having a successful social taboo against Ptolemaic astronomy feels from inside.
"There are no good arguments for Aristotelian physics" is simply how having a successful social taboo against Aristotelian physics feels from inside.
There are in fact good arguments for all three of those theories, and better arguments against. I'm guessing you don't know either arguments, and base your belief in all three based on argument from authority.
Edit: Also the situation isn't exactly analogous due to the difference between debates about physical facts, and debates about policy.
Ideally, I would estimate the negative effects: how many people would later learn I lied and abandon my cause, and how enemies of the cause might use the fact I lied against it, and the reputational harm to my other causes and to my allies.
Not to mention the damage the people who believe your lies might do by acting on them.
What might be the cause of the perceived difference between the atheists/nontheists in Europe and in the USA?
Where in Europe? Richard Dawkins is from England and organized things like the infamous atheist bus campaign.
Also numerous European countries used to have atheist militants, of the priest-killing or at least send-priests-to-labor-camps variety.
Well, in case you haven't noticed aren't in small forager tribes right now.
You're right, I left out a few alternatives. We could also deport them to a haunter-gatherer society, let them go around engaging in tribal-style raids (although that tends to interfere with the functioning of modern society for those who can function in it), or let them starve to death.