[EGreg]

Read what I wrote carefully. For things that you need to convert to human-readable dates, by all means use UTC.

But for timestamps that can be used to obtain a time difference between them, TAI should be readily available to be used. Most timestamps are for figuring out time differences here on Earth and not relative to astrological signs, they are for knowing what came before what, etc. They are not for generating human-readable dates. It's silly that such a major use case is hardly implemented on major systems, and instead an unreliable Unix Time is used which can "at any moment" have the same second twice.