I've been on US domestic flights in which the seats were so close together that the person reclining had their face below mine, in my lap. I would prefer to agree with you that if the seat reclines you should be able to use it, but the reality of what the airlines have done to pack in more people makes it physically painful for other passengers when you do. The airlines have done an excellent job turning us all against each other, when this problem is of their making, out of pure greed.