Will they? I'd actually be surprised if there are many people that, upon receiving a suspicious message from someone who claims to be Joe Schmoe, will actually go and check to see if a different account from Joe Schmoe with a blue check. I think it's much more likely that they're either going to recognize it as a scam right away, or they won't and they'll fall for it. In either of those cases, it doesn't help for the blue-checkmark-holder to keep their account.
There will always be someone falling for scams. No amount of safeguards will protect them if they do zero due diligence and the scammer is persistent enough. The checkmark isn't an end-all-be-all, but it's another small step someone can use to verify without too much hassle.
also, I just noticed "they" is ambiguous here. I meant "the twitter staff giving checkmarks". At least I hope they do some basic check before handing out a checkmark to an obvious impersonator.
