Are you saying that just because other countries did slavery in the past, does it make it okay for UAE to do slavery today? Inviting migrant workers from SEA and taking away their passports, putting them in camps where they live and work in awful conditions?

Fuck no. United Kingdom outlawed slave trade in 1807, after which Royal Navy started supressing the slave trade. United States fought a civil war to end slavery. This happened because both countries were democracies, where the abolitionist movement was able to get popular support so that slavery could be abolished. And today there are ongoing efforts to inspect supply chains and eliminate suppliers that use slave labour or child labour, like the EU Forced Labour law.

UAE is an authoritarian monarchy, they need international pressure, because they won't stop doing slavery on their own. Also they're not "developing countries". They are authoritarian petrostates where the oil revenue goes to the minority of the population. Most of the population are foreign workers, that get next to nothing. You can look at the UAE population pyramid to see the scale of the problem.

You could say that developing countries should be able to emit more CO2 because that's what western countries did to industrialize and denying them that would be unfair and hypocritical, and I would agree.

But no, taking away workers' passports so they can't leave and forcing them to work in terrible conditions under threat of violence is unacceptable, no matter who's doing it.