When large regions of ice melt, it changes the distribution of mass in that region, which lowers gravity in that location, which in turn lowers the ocean level (but of course there is more water overall). There is redistribution of that ice as water mass elsewhere on the planet, which increases ocean level more in the remainder of the ocean, and changes gravity elsewhere. It’s not just a matter of mean rise.
The greater the amount of melting, the more gravity will fall in that region, which means not only will ocean levels rise everywhere because of more water, but it will rise more the further away we move from the location of the melting.
This could all happen as a consequence of warming, which is why it would be wise to be conservative in estimating the factors associated with warming, and to clamp down as tightly as possible on any source that could contribute to warming, and to use technology to change the way we make energy, with emphasis on sustainable renewable energy.
What is the worst that can happen if climate scientists are wrong about the factors associated with global warming?
It is inevitable that peak oil will be reached as some point ... by accelerating the rate at which we switch to other sources of energy, all we are doing is preparing better for the change that must happen anyway. Why not make that change sustainable, so the entire ecosystem can remain?
What is the worst that can happen if we do nothing?
It is not conservative to do nothing. To be conservative would be to do the wise thing, without waiting for hindsight to say “we should have done something”.