Why did they want to kill Tucker?

I really enjoyed this film but it had a few flaws. For example, I felt that the lesbian nuances were shoe-horned in to appeal to a political peer group that otherwise might not have given this film a second glance. Kind of like making a leading man black, in other movies, in order to attract a black audience. Not necessary to the plot, perhaps, but economically sound.
Another flaw was the motivation behind wanting to kill Tucker. Was it becaue her irradiation by the H-bomb had polluted the code of other time travelers? Well, killing her AFTER the fact helps no one. And the simplest solution to that problem was the one Drew executed.
If anyone knows why Tucker needed to be killed please respond.