Re: Man Of Steel Tie-In Comic *GIRL OF STEEL CONFIRMED*
If he was afraid of tackling characters that some people find silly he wouldn't be involved with Batman and Superman in the first place. Neither of them exactly had glowing reputations in the public eye before their respective reboots. Batman had ice puns and Superman had the "he's an owerpowered goody-two-shoes" thing going against them. And I don't know why you'd assume he'd be opposed to Supergirl, she's not inherently silly, just like Robin. There are some silly aspects, but they could easily be played straight without much sacrifice. She might not have her comics costume, but like Robin, she'd still embody the character at heart.
But none of that matters because she probably wouldn't show up until the sequel and we don't even know if Nolan will be involved come the sequel.
2011: "This movie sucked because of executive meddling."
2016: "This movie sucked because it didn't have a designated meddling executive."