Are you sure that's what has been said? That they might be re-purposed for delivering nuclear warheads? That's crazy.
Their use in assisting a US first strike would be to help neutralize Russia's offensive threat, making whatever retaliatory response Russia could muster that much more survivable. From Russia's point of view, that's bad enough.
It's the sort of thing that was always a big roadblock to disarmament in the eighties, when people still cared about disarmament. You need to coordinate bringing up defensive weapons with retiring offensive weapons in a way that preserves some strategic balance, and if one side doesn't have the right sort of defensive weapons, or a good place to put them... It's why notions like the US partnering with the USSR to deploy defensive weapons were publicly floated.
“A President of the United States could offer to give that same defensive weapon to them to prove to them that there was no longer any need for keeping these missiles,” explained Reagan. “Or with that defense, he could then say to them, ‘I am willing to do away with all my missiles. You do away with yours’”