It doesn't matter if autodesk gave it away in my opinion. As a user, you are contributing to software just by using it and talking about it, by reporting bugs, etc. In one case, all that feedback goes into making the proprietary software better, and when you get older, you are more willing to pay huge sums for it (like what apple did). In the other case, you make software better that benefits everyone, not just those that can afford 4 digit licensing fees.

Considering that, I have to agree it is unethical in this case to teach proprietary software