I firmly believe that you deserve to enjoy all of the space you pay for. You pay for the seat, the area in front of it where your feet go. And you pay for the sliver of room that encompasses the recline of the seat. If somebody in front of you reclines, you should recline your own seat -- then you have more room. If you sat in a row that doesn't recline for one of many reasons, then you are out of luck and will hopefully learn to insist on being seated in a reclining row in the future.

Of course, if somebody asks you politely to un-recline, you may choose to do so. I always have handy excuses for various requests, such as:

If they ask you to un-recline, tell them you have a back problem.

If they ask you for your window seat, tell them that you are claustrophobic and need the view, otherwise you'll freak out (they won't want that).

If they ask you to switch meals, tell them you have a special dietary/medical reason for eating that meal.

If they try to put stuff under the seat in front of you (i.e. where your feet go), tell them you have a knee problem and need to stretch out.

Again, if they ask nicely and it's not too much of an imposition, you can always grant your request -- but it's best to have your ammunition at the ready if you don't want to grant that request.

As for seat kickers, tell the parents that you would appreciate if they could ask their child to stop. If the kid persists, tell them that you've been flying since yesterday morning (having come from some far-flung place) and you are really trying to sleep. Then, they become the bad guy, not you.