The only point I was trying to make is the following:
If you tell the population "Starting next week, we will do everything an hour earlier. You get up an hour earlier, your work starts an hour earlier, the supermarkets start an hour earlier, etc..." people's reaction is "What? I don't want to get up so early! I want to get up at 7, I don't want to wake up at 6!
But when you say that next week we move the clocks an hour forwards so now you have more daylight in the evening, most people are enthousiastic about it. While it's exactly the same thing, just packaged differently.
I live at a 54 degree latitude. The changeover to summer time causes a measurable spike in accidents every year, just to mention one negative effect. It's only good for a couple of months during the summer. In the spring, it means kids going to school when it's still dark etc. The negatives outweigh the positives.
When I said "wake up an hour earlier", obviously I meant "and go to work an hour earlier". The two scenarios are identical then: either we tell everyone to start work an hour earlier, or we tell them to start at the old time but move the clock an hour forward. When you give people the choice, many hate the former but love the latter. Go figure...
I'm actually an airline pilot, so I am very familiar with the unhealthy effects of time shifts (extremely early wake-ups or late shifts, night flying on long haul, etc.).
Look at this study: it found a clear increase in cancer risk as you move towards the western part of a time zone. When you cross into the next time zone, the risk suddenly drops and then creeps up again as you continue to move west. You can actually see the time zone borders on the chart of cancer incidence. Every 5 degrees of longitude corresponds to 3-4% increased risk of cancer. Summer time corresponds to 15 degrees...
Yeah, if you ask people to wake up an hour earlier in the summer, they'll reply "no, I can't, I'm not a morning person". But when you set the clocks forward by an hour, they're all happy because they have "more daylight" in the evening which is great because they're not a morning person. Go figure.
GMT wouldn't make a difference. Americans are not going to get up at 7 am GMT when it's the middle of the night for them. So instead of saying "what time is it over there", we'd be asking "what time do they get up there, what time do business open there, 3 pm?". At least time zones make it clear what time of day it is, with business hours being pretty much the same everywhere. Also, having the date change in the middle of the afternoon is not exactly ideal either.
Funnily enough, your very point that plants and other living animals waking to a rising sun don't give a shit goes against your argument that everyone should be using GMT. We should be using a local time that is not too far away from solar time. So winter time.
All extremists should be taken out and shot.