We need to understand that there are 7 billion people on Earth and we need to communicate to ALL of them, lest you want Trump/Johnson/Salvini/etc. reactionary movements dismissing climate change or complaining about actions. 1mm ocean rise asks for being ignored. Why not address direct effects to people? People that die, migrate, wars... how many dead people implies 1mm change? That would be much more useful.
That’s not the sort of slogan that’ll likely motivate a lot of change.
That’s ignoring the potential for runaway feedback loops.
I’m just saying that it didn’t, in fact, cause much change, as evidenced by the business-as-usual scenario we find ourselves in seven years after 2012.
The more that melts results in changing albedo and smaller thermal mass to encourage an accelerating melt - a small runaway feedback loop. Rising air and sea temperatures will accelerate it further.
You and I may not care that much - yet, but those in the Marshall Islands, Maldives and other low lying regions almost certainly care about every millimetre. Sea level rise is probably the least dramatic effect of climate heating, but the most inexorable. It takes a while to melt 650,000 cubic miles of ice, yet we seem to be managing to get going. It will accelerate.
It should be cause for major concern.