To play Devils Advocate, but I can easily say that people with visual, intellectual, or sensory problems/disabilities may find it difficult to discriminate amongst boy-girls toys if they are sort of lumped in the same category. For example, we know people with autism prefer things to be organized very specifically. When they are not, it causes them severe distress. Having boy and girl toys mixed together may interfere with the typical patterns that people with autism associate with certain genders. Or if there are no signs, people with sensory problems (visual) may find it more difficult finding certain toys, if there is not a sign that says "boy toys." If all the toys are lumped together, they may find it difficult to discriminate between a boy and girl toy. For MANY people, having things specifically categorized makes life easier, especially those with some sort of intellectual or sensory deficit. I can definitely see how mixing boy and girl toys together can make it difficult for someone who is intellectually challenged.
So, its totally okay for Target to do this, without due regard for how it may affect other people? Hmmmm. Seems like these people who are bitching and moaning have no heart for how it may affect other people. But, thats okay, because they got their way.