I'm sure this isn't a great argument, but I went with it anyway.

One possible objection to contractarianism, is that there cannot be enough practical agreement among rational agents at all to get the kind any kind of general moral principles. There are many issues, given even perfectly rational beings would still viably disagree on. It would be hard if not possible to create any over-arching principles of morality. Things would have to be a case-by case basis. This may not be a problem, It may even be a strength of the theory. But if the point and purpose of Morality is to be action guiding, it would be much more practical for there to be easy and simple rules to follow. Take for instance abortion, it is not irrational to chose to be either pro-life or pro-choice. A perfectly rational being can lie on either side of this decision. One could augment this, perhaps if the bargainers had perfect knowledge. But even then, I’m not convinced that there will necessarily be no room for issues with more than one rational answer. This may not be a problem, the ideal contractarian might say, because such cases would be rare, and on the whole perfectly rational and perfectly knowledgeable beings would agree on most things. However, If you are anything other than an ideal contractarian, I think there is a big problem. Imperfectly rational and imperfectly knowledgeable beings won’t agree on too many things. Not only would there not be a consensus on the general level, but it isn’t even clear that in the individual or local case that imperfect rational beings could agree on what someone should or should not do. The contractarian might reply that “look, we don’t mean people will agree on everything, but generally most rational people WILL agree on some basic things, and that’s good enough.” But what basic things are these on which most people will agree to them? Even common sense morality is rationally objected to by the many and the thoughtful. I think, that, aside from appeal to idealism, there will never be any real solid and generalizable agreement contractarians can conjure from the disjointedness of real humanity.