I agree on this to a extent, I have no beef if someone's selling models of stuff they truely can own right to or no one holds rights on, Like say animals, figurines, fantasy objects, etc. And once you make it available for everybody you screwed the creator. You do not need to rip models - you will learn nothing. I dont want to become rigger but its so well done that its hard not to at least give it a try.
In YT you have full series about rigging - in fact I am going through one of them now. If you want to learn there is so much things for free already its absolutely mind blowing. To finally become poor Indian trying to sell his stuff on internet but being screwed by some other poor Indian who "wants to learn". In order to do so he will take models of other poor Indians for free.
Its always the same - now he is poor student from India who wants to learn.
rig or whatever floating freely on internet your perspective changes. But I promise you - the day you see your model. As long as you are the one who is taking somebodys work for free it all seems fine.