The possibility that someone is doing it mainly because they feel they have to because of the inherent financial pressures they find themselves under seems pretty bad. It's also bad for other jobs too, for the same reason; it is a consent issue, you aren't really consenting if you don't actually have a choice between the work available to you or losing housing/food/medical care etc. There's also the more prevalent issues with potential human trafficking with sex work. I don't think it's really ethical to pay for it given that stuff, but maybe it could be in a society with way more guarantees and protections.