If orion had politically one out and been weaponized it would make current MIRV technology look like a BB gun. Threat of it's development might have triggered a preventative first strike. You can make up all kinds of hypotheticals for either way.
See my parallel answer to 'molbioguy'. I would argue against your point (mainly, you don't need that with icbms + fusion bombs; more than a factor of ten in killing the enemy is a waste of money), but it isn't relevant to my point regarding the Fermi paradox.
