If the problem of the polar and antarctic ice melting raises the sea levels why not build giant desalination plants?

Before you say "well that will never happen because it's too expensive", we have an amendment in our constitution that allows slavery in the form of prison labor, I mean instead of prisoners booty banging each other or killing and stabbing each other, why not take the strongest prisoners we have and use them in constructing ginormous plants that take in sea water and turns them into fresh water the same way the Egyptians and romans used slave labor to build their monuments and society?
If the problem of the polar and antarctic ice melting raises the sea levels why not build giant desalination plants?
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