I will concur that it is very bad business to cancel legislatively cancel contracts without good cause that would be recognized by any possible party with whom a contract might ever be entered into.. which essentially is everyone.
But, as for your assertions that marriage contracts were not explicit, that's just plain silly. You've handled yourself well on the forum, so I hate to call an assertion silly, since it doesn't afford the respect you're due; but, call it my own incompetence, I can't think of a better way to put it. It's not only false, it's outrageously false. Marriage contracts clearly specified their terms, despite the fact it was vey unromantic. Every last living soul expected that, yes, you must pay alimony if you break the terms of the contract, even if they didn't think of it in such terms. And they even ritualized the summation of the contract, so the summation wouldn't seem so gosh-darn unromantic. ("I, Dan, do solemnly swear...") The terms were in writing, were universally understood, were fully representing the spirit, and were part of our social fabric.