This product is like covering up your neighbors reading light because it bothers you. It's not yours to turn on/off. Lack of space is part of air travel, if you can't fit your laptop on a tray that is reclined then pay for first class or get a smaller laptop.
There is worse behavior on planes of course. I was once on a flight where I put my backpack under the seat ahead of me and the woman sitting in that seat started kicking it. I firmly pointed out to her that there was a laptop and camera in the bag and that she needed to stop. She informed me that the space under her seat was hers and that I needed to move my bag. The dispute finally ended when she hit the call button and the attending flight attendant eventually had to have her removed from the plane.
A flight on a plane with smoke in the air.
I don't think these are strict rules or anything, you are certainly entitled to do whatever you wish, it's really just a question of politeness.
Sure, out of politeness I might refrain from using the intended functionality of the seat if you ask nicely (same goes for switching off the light or redirecting the airflow nozzle, and I might choose to delay my toilet break to avoid disturbing your sleep). My sense of politeness tends to go out the window when people start suggesting its selfish or impolite for me not to coordinate my cabin controls to their liking.
That the seat is designed to work in different positions has little to do with whether or not it is rude to use some of those positions. Rudeness is in general situational. An action that is fine under some circumstances can be rude in other circumstances.
For example, my home theater is designed to make very loud sounds. Are you going to argue that this means it can never by rude of me to listen at top volume?
My digestive system is designed to expel noxious gases. Do you think that justifies farting in crowded elevators?
It's usually not that you can opt out of this. Would be cool though: left aisle: no reclining seats, right aisle: reclining seats. :)