Homeopathy and naturopathic health cures. The only argument for these is that they work as well as a placebo.
Cosmetics and jewelery. These are particularly expensive mate attraction and social standing boosters.
Lobbying for government handouts/boons/subsidies. These have the potential to have net utility, but in many cases do not.
Monopoly businesses. Net loss of utility through inefficiency.
And finally, an overarching overemphasis on reliability. By declaring that 'failure is not an option', we spend vastly more resources than if we were to simply accept failure as an option and properly handle the failure cases. The best direct examples of this come from information theory: it is almost always cheaper to add error correction to reduce the error rate on a channel, than it is to improve a channel to reduce the error rate without error correction.
"Monopoly businesses" is a rather broad category. And "net loss" compared to what? Compared to if they were operating differently, or compared to if they weren't operating at all?
This is an offshoot of a thread I made earlier, but which wasn't eliciting the sort of responses I'd hoped for.
So let me pose a clearer question with less potential to get people on watchlists.
What legal ways of making a profit are the most anti-altruistic, the most damaging to society, the opposite of effective altruism in result.
I am using utility loosely. The answers need not be given from a utilitarian perspective at all, but instead merely deal with any means of making a profit that seems to you clearly wretched, and such that the world would be better if nobody participated in it.
I'd also like to emphasize that these things should be legal. There are some obviously wretched illegal businesses that would top the list otherwise. If something is legal but only in a particular jurisdiction, then you should only discuss it within the context of the jurisdiction where it is legal.
If it's a grey area, go for it, but extra points for society-harming enterprises definitely legal in both the letter an the spirit of the law.
This is NOT about whether the enterprise in question should be illegal, just whether it causes a net loss of utility (deal with counterfactuals however you see fit).