Why the continued obsession in measuring the year as a multiple of days? Pick a any notion of year and any type of day measurement.  Outside of history and the common cycle of day an night, why are these viewed as integrally or even fractionally commensurate?

Why all the stunts with leap days and leap seconds, etc... when we now have atomic clocks?  Why not decouple the two?
Why all the stunts with leap days and leap seconds, etc... when we now have atomic clocks? 


Science exists to serve mankind, not to rule it. Calendars were one of the first concepts developed by humankind, arguably predating writing. Timekeeping is even more important to modern society than it was to the ancients. You're not going to get rid of calendars.

One key purpose of the Gregorian calendar is to keep the calendar in sync with the seasons. Every solar calendar requires some intercalation mechanism. The Gregorian calendar uses leap days. The Gregorian scheme (years divisible by 4 have an extra day, except for years that are multiples of 100 that aren't divisible by 400) will fall out of sync with the seasons at at the very slow rate of one day per 3030 years.

Leap seconds are a rather different beast. They are inserted, unpredictably, to keep the clock in sync with the day/night cycle. Without leap seconds, counting 86400 atomic clock seconds = one day would already have the clock out of sync by about half a minute. Leap seconds are problematic for business. There is an ongoing effort to remove leap seconds and just live with a day of 86400 seconds going out of sync with the day, at least until it truly becomes noticeable.


  Why not decouple the two and say that day X belongs to year Y if at 12:00 noon of that day is "in" year Y?


What's this "year Y" thing you're writing about? How do you know what year it is without a calendar?