G'ahhh! Not again. Not the "it's going to ruin my happy married sex life" argument. No it isn't. It really, really isn't.
NCIS (love the name by the way) - this is like the thing that always comes up re. discussions of initiating sex while one partner is asleep. Again, it's not bloody rocket science.
Scenario 1: You're happily married. At some stage one partner says "you know, I have a bit of a kink where I would quite like being woken up by you starting to make love to me... and don't worry, if on the odd occasion I'm not in the mood, I'll let you know, and so long as you stop if asked, which I know you will, because you're a nice person who loves and respects me, that's fine." This is perfectly OK.
Scenario 2: Abusive marriage - one partner routinely wakes the other up by "climbing aboard" despite having repeatedly been told that this is not welcome. Sexual assault/rape.
Scenario 3: The morning after the night before in what started out as a consensual one-night-stand. Just because they had sex the night before, you can't assume they'll want to have it this morning - you have to wake them and ask, and if you don't, again, sexual assault/rape.
Honestly, normal, reasonable people can quite easily tell the difference between a sexual advance which is welcomed and reciprocated and one which isn't. In fact (google the work of psychologist David Lisak on date rape) rapists can tell too - they just don't care.