Actually, Mick could have said "Let's spend the night together" on TV, but not without "consequences". The show went out live, so he could have sang or said anything he wanted, and as far as I know, they didn't even have tape delay back in those days. It was Sullivan and/or his producers (or possibly some network executive) who objected to the lyric, not the FCC. As far as those consequences go, The Doors were banned from The Ed Sullivan Show because Morrison sang "Girl, you know we couldn't get much higher". But that's all. They still appeared on other TV shows, and their career doesn't seem to have been affected too greatly by said ban. Personally, though, I think Mick rolling his eyes as he sang "Let's spend some time together" was more subversive than Morrison singing Light My Fire as originally written. Mick was subtly acknowledging how outdated the "standards and practices" around such things were.