The Soviets had a "no first strike" doctrine because they perceived themselves to be the stronger force on the continent. They had a huge standing army and massive numbers of armored vehicles and expected to be able to roll through the fudla gap and across western Europe as they had done through Eastern Europe in the final stages of WWII.
replyNATO, on the other hand, expected to be overrun by the soviets and used the threat of nuclear counterattack to keep them from trying it. The Soviets built up their own nuclear deterrent to prevent NATO from responding with nukes (the MAD).
If the US/NATO nuclear threat wasn't credible and the NATO armies were no match for the soviet army, then western Europe became a pawn for the soviets, leading the western allies to also invest in conventional arms.
In short: the argument for the conventional forces was that the nuclear threat wasn't really credible because nobody would choose to end the world.