Here's what I don't understand about abductions. Supposedly they have been abducting humans and probing them for centuries now. Surely they, Mr. Interstellar Travellers, have found out everything there is to know by now? They are already FAR beyond us in science and probing science and yet they still keep scooping people up and examining them.
How many cows do we dissect to find out more about cows these days? And we're primitives!
I can't help but suspect there is some sadism involved here. Either that or they are getting paid by their authorities for the "research", like the Japanese with the whales.
Perhaps there's something they need from those animals....some sort of nutrients, maybe genetic material or something. I also think with people, they are keeping eyes on them how they are, like when we catch and tag and animal and release them. And as I mentioned, we're dealing with aliens, whom might have a completely different mentality than we do. Also, I have heard of various hybrids being made and they are let into our own world and blend in, it's a pretty interesting way to learn things....also, I have seen really weird looking folks and gotten.....interesting vibes, like they are really not from around here. Maybe they are also tying to improve themselves and/or ourselves.
Also, like I said, some are probably good, some are probably bad. We gotta learn about them and be aware of their existence first before getting all the other answers.