Of course there is - only someone completely ignorant would claim there was "nothing" rude about it. If you feel you have a right to use it simply because it exists then by all means go ahead, but by doing so you restrict my space so much I can often no longer move my legs and have to have my knees pressed against a hard surface unless I sit with my legs curled up on the seat. I'd love to hear your explanation as to how that isn't rude whatsoever?

And there is an enormous difference between life threatening and a "safety risk"... I agree with you more than then, but however negligible it is, I guess restricting the ease of movement in the row behind you could be classed as a safety risk - presumably why seats backing onto exit rows don't recline.