With separate accounts, a homemaker stands in a much weaker position than the primary breadwinner. A shared account–while not eliminating the power imbalance–shifts power to the spouse who earns less, because now the money is theirs. In a shared account, it matters less which spouse earned what; they are now an economic unit. The money should be shared equally precisely because the labor is not.Having separate accounts does not preclude the possibility of having a joint account for joint expenses. Neither does it mean that both spouses must contribute the same number of dollars to the joint account regardless of differences in their earnings; they could each chip in a set percentage of income instead. A shared account may enable married persons to spend beyond what would otherwise be their means, but to state unilaterally that shared accounts shift power to the lower (or non-) earning spouse ignores the very real psychological issues in a marriage that stem from one party having what is perceived as more of the power and control. Heidi's observations about how pooling all expenses made her feel monitored are a great example of this. And the Family Scholars, like Brooks, ignore the huge costs that joint accounts can impose on a marriage that ends--an abusive spouse may drain the joint account so his wife cannot leave, or a widow may be temporarily broke when her dead husband's accounts are frozen (examples from the comments here). But even discounting these worst-case scenarios, there's no reason to get exercised about some modest financial independence in a marriage, if that's what makes the spouses happy.
Even married couples have some privacy from one another, unless the Family Scholars use the toilet with the door open when their spouses are around. Even the most loving couples need time to be alone sometimes, otherwise a night out with the boys/girls is somehow anti-marriage. Having separate accounts is just a financial analogue to the other little ways in which even married people give each other a little space. If you are comfortable inviting your spouse in for a conversation while sitting on the can or if you don't mind having your husband be able to count in Quicken every cup of coffee you bought, that's fine. But please don't press your unity-at-all-costs philosophy on those who are less financially gregarious.
P.S. Interesting discussion of a problem indirectly caused by joint accounts here.
UPDATE: Phoebe points out that the separate account may be a ticket to nowhere for some abused spouses. Maybe, but not all abused spouses don't work or have a minimal work history, so they could have an opportunity to squirrel some money away. And frankly, if someone is a penniless, skillless, jobless SAHM with a husband who demands that everything be in a joint account and is free with his fists, I don't have any qualms about encouraging that woman to systematically steal money from the joint account and sock it away someplace safe until she has enough to get out on her own. Your rights stop where my nose begins, and all that.