You don't need to always use UTC to get the benefits you describe. Just always give times in UTC when communicating across time zones. The only disadvantage is that the receiver might not know how to convert from UTC to local time. This is basically the same problem as converting people to UTC, however. At least this way the receivers know they need to look up the conversion, rather than thinking they know but getting it wrong due to DST or whatever.
In every situation where the time zone is not obvious, it should be included in every statement of time. Obvious would be communicating with someone in the same time zone where we both will be in the same time zone at that time. Non-obvious would be communicating with unknown parties that might be elsewhere, especially over the internet, but even a physical bulletin board would count if it was near a time zone boundary.