My coblogger David Bernstein wrote, in a comment to my preference-for-agnostic-parent hypothetical,

It strikes me that if there is uncontested evidence that the parents agreed to raise their children in a certain, nonabusive way when they got married, the parent that follows through on the deal SHOULD be favored, whether the agreement was atheism, or religion, or whatever.

Here's my thinking on this. I'm generally a believer in enforcing contracts, even when a party changes his mind about them. The power to enter into binding contracts is an important power.

1. Nonetheless, precisely because contracts are binding, the legal system has to distinguish contracts that the parties intend to be legally binding from plans or tentative agreements that express a party's current views but that don't purport to legally bind the party in the future. "I will always love you" said to a lover is a classic example: If you want to make it legally binding (even to the limited extent that marriages are legally binding these days), you have to go through some pretty significant formalities. Without those formalities the agreement is understood as expressing a desire, a hope, or a plan, not a legally binding commitment.

Likewise with "[Christianity / objectivism / music lessons] are an important factor to me, and I feel strongly about raising our daughter this way." One can be entirely sincere about this, and in fact plan to stick by this, without intending to make a binding commitment. In fact, many people -- knowing how time and experience leads us to change our views on many subjects -- would rightly balk at making such binding commitments (just as they often, though not always, balk at turning "I will always love [my boyfriend/girlfriend]" into a binding commitment).

So if there is evidence that the parents agreed to make a binding commitment to raise their children in a certain, nonabusive way, there would be at least a serious argument in favor of enforcing the contract (though one would need to know to what extent the best-interests test can be displaced under state law by such contracts). But it seems to me a mistake to infer such a binding, long-term commitment simply from an agreement in principle, as to matters on which people's attitudes often change with time.

2. It's also important that contracts, especially contracts about religion, are clear enough that courts can sensibly enforce them. An agreement's vagueness is often a sign that the parties didn't intend it to be binding. But given the Establishment Clause constraints on theological judgments by courts (even when the courts are interpreting contracts or wills that expressly call for such judgments), it's especially important that the contract be clearly applicable using the court's strictly secular interpretive approach.

My sense is that many casual agreements about religion or the importance of religion are not sufficiently clear. "I agree that we should raise our child Jewish," for instance, leaves a great deal uncertain. Obviously, the particular strain of Judaism isn't mentioned. Neither is the intensity of the raising -- does it mean that Judaism (whether Orthodox or Reform) would be a pervasive part of the child's life, just that the child would be exposed to some of the most important aspects of Judaism (i.e., become a High Holidays Jew, though perhaps with a bit more intensity around Bar Mitzvah time), or something in between? Neither is the specific degree to which the raising would involve organized religion, rather than just individualized study. Neither is the degree to which the child would be exposed to rival views (which may become important if the parents divorce and one converts to a different religion, and exposes the child to that religion without otherwise interfering with the child's religious rituals).

Now each of us can have a sense of which side is complying more closely with even a vague agreement. There might even be a good deal of consensus on the subject. But in such cases, I don't think this sort of consensus is an adequate basis for courts to decide, because it involves too much subjective judgment about what are the "true" rules of certain religions, and which of those are "central" -- something courts are barred by the Establishment Clause from doing.

For instance, is an agreement to raise the kids Jewish violated by a parent who tries to raise them as Jews for Jesus? I know that many Jews believe it would be, and in some sense they might be right. But I don't think that a secular American court is allowed to decide whether or not Jews for Jesus is "really Jewish," whether Reconstructionist Judaism is "really Jewish," whether Reform Judaism is "really Jewish," or for that matter whether Mormonism is "really Christian."

So it seems to me that even if the parties are intending to create a legally binding agreement (which they often won't be), many kinds of religious agreements would still be unenforceable by secular courts. Perhaps some might be, for instance an express agreement that the child would be sent at least twice a month to churches of a particular organization, or an agreement that the religious terms of the agreement are to be subjected to binding arbitration through some private religious body (such as a Jewish Beth Din). But they would have to be drafted in such a way as to avoid the need for religious decisionmaking by a secular court.

3. Finally, I should note that if one thinks the court making a custody decision should mostly focus on the best interests of the child (subject to whatever constitutional constraints there may be), then it's not clear to me to what extent the court can consider the parties' contract, which need not be aimed at the child's secular best interests. (Sometimes departing from such a contract would be against the child's best interests, but not always and not necessarily even most of the time.) But one could certainly argue that state family law should sometimes subordinate the best interests standard to reasonable agreements between the parties -- setting aside the other objections I raised above -- especially when enforcing such agreements can often yield more certainty, quicker and cheaper resolution, and decreased acrimony.