Challenge: If you don't believe that Jesus atoned equally for all the sins of every individual without exception, you can't call anyone to Christ for salvation, or even know that He died for you.
Response A: Hunh. Well, I guess that's true... in a way. I mean, apart from Jesus calling all men to come to Him, saying that none can come except the Father should draw Him, promising that He would never cast out the one who did come to Him, identifying these ones as the ones the Father gave Him to save, assuring that they would never perish nor be snatched from His hand and that the Father loves them just as He loves Christ — apart from that, I guess we really don't have anything solid to stand on. You know, beyond Christ's specific, conditional promises.
Response B: Hm. But if you do believe He equally atoned for the sins of Judas, the Beast, Peter and you, you don't have any assurance that your sins won't send you to Hell. Poor trade-off, that.