Is Morality Important in a Partner?

"Dear Prudence" at Slate says a one time moral blunder is okay, I say it's a warning sign. "Mr. Goody Two Shoes" writes Prudence, concerned that his girlfriend is a thief:

The other day my girlfriend of three years told me that she found a wallet with over $200 inside. When I asked her what she was going to do with it, she said she was going to keep the cash. When I asked her why, she responded that she "needed the money." While I can understand finding that much money just laying on the ground doesn't happen often, I am somewhat disappointed and shocked by the lack of ethics in her final decision (even though we are both pretty broke at the moment). I even had to plead with her to anonymously mail back the person's driver's license and other contents of the wallet because it was a generous thing to do. Part of me just wants to forget the whole thing ever happened, while another part of me tries to make her feel guilty for being so misanthropic. Are opposing moral views something I should just accept within our relationship, or is this a sign of a deeper issue?

Prudie's response?

...... But your next move should not be to try to make her feel guilty, but to get her to understand why you were so disturbed by this incident. Tell her you don't want to keep flogging this, and after this discussion you will not bring it up again, but what nags at you about the whole thing is how out of character it was for her, because she is a thoughtful, considerate person. You can add that you know that if she accidentally left her wallet somewhere, she'd hope the person who found it would return it intact. Obviously, you're looking for her to say that you're right, and that she realizes she made a mistake. She may feel so defensive that she can't do that now, but maybe after mulling it, she will. Keep your promise that you will then let this drop. You've known her for three years, so unless other evidence presents itself, consider it a one-time lapse.

Hello? The girlfriend should feel guilty, she took someone else's money and then had no qualms about never returning the wallet. This is not a one-time lapse, it is a window into how the girlfriend ticks. Understanding how someone operates when under stress or when no one else is watching is important. It tells you how they will treat you under the same circumstances. The girlfriend said she took the money because she needed it, what if this couple gets married and this woman needs money or something else in the future, will she just take it out of your joint account when you're not watching even if you don't want her too? If she gets desperate enough, what else will she do? Perhaps this guy doesn't know this woman as well as he should.

I would tell him to take this behavior as a warning sign and to keep it forefront in his mind. Does he plan on marrying her at some point? If so, I would tell him to have a looooonnnng engagement because watching how she responds to that stress might tell him even more about what kind of person she is, or isn't. It's better that he find out about her lack of morals now before he is sitting in divorce court, or worse, in a loveless marriage wondering how he missed the warning signs when they were right in front of him all along.