As has been pointed out already, you’ve either misread or the people who said this misread themselves. The worry is about ice on land (Northern Canada, Greenland, Siberia, etc.) melting and running into the ocean. Ice which is already floating in the ocean won’t affect the overall depth of the ocean as it melts.
The last IPCC report that I looked through also predicted no more than a maximum of 2-3 feet of gain in depth over the next century or two. While this is problematic to people who live very near to the beach and the Netherlands – the whole nation is at or under sea level already – it’s not a catastrophe in itself.
Where there would be a greater worry is that larger, warmer oceans will have a greater effect on weather. Hurricanes are, effectively, powered by the ocean. If the ocean has more power to give, then you get stronger hurricanes. With an overall faster wind speed across the globe, this will generally make cooler climates colder and warmer climates even hotter (temperate climates will shift towards warmer.) This plays havoc with ecology. In the US, changing out what plants are grown in what regions isn’t too difficult, but in the majority of the impoverished world, a shift in what plants are sustainable is hard to maintain.
Overall, of effects that we expect from data, in the US and Europe, the main issue is going to be the cost of adaptation. Houses which have been hardened to modern day hurricanes will become insufficient. Prime farming territory will move out of the US West Coast and into the Canadian West Coast. Some number of lives will be lost to historically unparalleled storms during the period of change. But, like Katrina, the vast majority of the population will be fine, and it will mostly be the poor and sickly who come to harm. Seeing as you’ve enough free time to argue politics on the internet, you’re probably not among these.
Catastrophe will mostly hit Africa and poor nations around the world – but not necessarily more than is already caused by simple tyranny and poor governance. Installing a better government and teaching modern economics to the general populace could likely do better for most of these areas than stopping global warming.
BUT, there is always the chance that significant, reallocated weight on the tidal plates will cause massive earthquakes and massive tsunamis – which are a lot less predictable and a lot harder to build for. There’s also the possibility that the raised temperature will cross some lynchpin boundary which could then cause a mass extinction event.
It’s also worth noting that most of the suggested changes for our nation to make, like transitioning to more fuel efficient vehicles, less power hungry light bulbs, a smarter power grid, and nuclear energy, are all more efficient and subsequently (in the long run) cheaper than what we have today (as well as reducing the amount of money that we pump into 3rd world nations). Even if climate change wasn’t happening or wasn’t caused by man, there wouldn’t be much value in arguing against the recommendations of the carbon-cutting crowd.