Resteemit is free. You can pay them if you will, which I do as often as I can afford. They just show your post to more people than you would be able alone. I don't see anything bad or unethical in that. Same with Minnow Support.
Resteemboss and such are more a pay-to-be-viewed services, so maybe less moral than the first ones.
But honestly : I know there are people struggling at writing good posts and other ones that just spam stupid things... I won't feel bad at seeing people like you or any working hard artist using tools that help them sharing their work and get many views from that.
I know there are also bidbots, but I don't think these are in this category... I don't know enough on the topic to be more precise though.