It's one thing to build a perfect model for how a society must operate but people have forgotten that people will often try to tinker with whatever model there is for their own agenda.
For instance the US founding fathers banned corporations - they hated corporations, indeed they fought a revolution to rid themselves of corporations. Yet here we are. I have wondered why they decided corporations were a good thing - perhaps it was because of the British industrial revolution, they didn't want to see their brand new country get their asses kicked by the Brits?
I don't know. So they undid the wisdom of the founding fathers and opened the US to rule according to corporate interests. This is the danger of having unbridled powerful interests. In the past they've had to act within the law but increasingly they have sought to be above the law.
A new manifesto must address the evolution of a society and new and unforeseen threats to the freedoms accorded to people.
Another issue the founding fathers never addressed was the equality of all people, not just (white) men.
That the interests of all people outweigh an individuals interest.
For some while I have been trying to fathom what is important to the right - and from what I can tell the right are only concerned with the interests of the first person singular, especially when it comes to white men, and extends to only to a limited domain which tend to be people (or perceived people, such as fetuses) that they care about. Seldom do they care about those less fortunate than themselves like the poor, or women in difficult situations.
I think the left is much more interested in us, as in first person plural, trying to empathize with others while still allowing people the freedom to choose as they wish. The right tend to police out-members of their limited domain, like women seeking abortions, women for not being perceived as attractive enough, women breast-feeding, women enjoying sex... for instance.