Premarital assets are already "protected" by state law in the event of a divorce. The only way they become marital or community property is if the owner gives the asset or part of the asset to his or her partner during the marriage.
As explained in the link I cited earlier, prenups are contracts that violate contract law by a) being coercive and b) lacking consideration.
I'm certainly no expert on all the state laws out there as they are a smorgasbord, what may be protected in one state isn't necessarily protected in another, nor can one foresee with certainty where one will ultimately end up living. If they do no "harm" because the premarital assets are already protected, what's the big deal in clarification to make sure both parties are on the same page?
As far as contract law, big deal. This is not a tit for tat type of "contract"/agreement, consideration is a mute issue unless one party is so egregiously harmed by the agreement it is thrown out. If it is "fair" and "equitable" it will be held up by most judges.
Also I thought shotgun weddings went out of style long ago so unless you can give me some examples of coercion when someone has the choice to marry or no, I ain't buying that argument. If one party says these are the terms I'm willing to marry you, take them or leave them does not coercion make.