Pascal's Wager is a gamble for a favorable afterlife built on one wild assumptions after another. If you use this, you're assuming there is a God first and foremost. Then you assume there is an afterlife. Then you assume there are multiple versions of the afterlife. Then you assume that belief can dictate where you go in the afterlife. Whether your assumptions are correct or not is no big deal up to this point, but that all changes when you assume that you know the very specific nature of God and what he wants from you. If you're wrong, then you could be the one forfeiting heaven just as easily as anyone else--Christian, Muslim, Pagan, Atheist, whatever. In fact, by making the wager you are worshipping a false idol, a damning sin in most deities books. The end result of the wager is the same for everyone. You are guessing at something that, if you are wrong, could earn you hell. Opting out of the wager is the safest move to avoid the "having other God's before Him" scenario.
The only reason to make the Christian assumptions is to accept the authority of the bible, and, let's face it, if nonbelievers did that then there would be no need for Pascal's Wager in the first place. Turning the gamble on it's head by assuming God will reward atheism and punish theism suddenly puts believers at risk. Why would God reward atheism and punish theism? I could answer "mysterious ways" here and make my wager just as valid as the next apologetic argument, but if you think about it, it is consistent with our own nature. I don't want my kids to worship at my alter, I want them to think for themselves. If I was an absentee father I certainly wouldn't expect them or likely want them to the look for me. Since God shows no sign of his existence, at least to me, He is like an absentee father, but if theists want to assume He's a narcissistic asshole as well, I hope they are comfortable in their very real codependency with a very imaginary master.