This is almost certainly a case of a guy just shooting off the hip, making an offhand comment that he thought about for .02 seconds. But, well, it's still news. From ESPN Los Angeles:
When asked if a player who tested positive for a banned substance should be stripped of the MVP award, Mattingly answered, "I don't know. It makes sense though, a little bit. It's not 10 years later, it's a month later."
On the one hand, I get the jibblies just thinking about the histrionics and posturing that would surround an MVP revote. A new phrase would enter the lexicon: the nuclear soapbox. And no one would care about mutually assured destruction.
But on the other hand, there have been under 150 MVPs in the history of the game. Mattingly was one. He has the membership card, the orange blazer, and the lifetime 40%-off coupon at Red Lobster. He's in. And while he didn't have the opportunity to take designer drugs, all he knows is that he didn't take them.
Now someone else is in the club, and he has the card, blazer, and coupon. He has also been accused of taking banned substances. It has to be just a little discouraging for a former player. It's human nature to think, "Well, if I had that stuff, I would have won six of those things."
It's also rare for a manager to offer any opinion at all, which is why this comes up.