I don't think that genetic engineering is a sin. The argument is that people are playing God. However, if God created the scientists, and the scientific techniques, then how can the genetic engineering be against God's wishes? There is nothing inherently otherwise immoral about it.
It depends upon what the religious point of view of what a sin is. Certainly there are those opposed to genetic engineering; as of yet, no one is forcing them to engage in it; neither should they forbid those who choose to engage in it from doing so.
The decision to endorse or reject genetic engineering as a science is a decision yet unfolding. There are many who regard scientists as assuming the role of God, while there are equally as many who consider genetic manipulation to be yet another gain for the positive as we try to master the world around us. At this particular time, there is no definitive trend that would either uplift or cast down genetic engineering as "sinning" from a religious standpoint.
I think the true sin here would be to neglect one's education, to stay in the dark, to be unaware, uneducated on exactly what genetic engineering is and what it's goals are. Whether you decide to support it or oppose it is a personal decision, but at least be knowledgable about the subject, and take a stand and be able to defend it.