For as intense as this debate appears to be, the "15 percent were unsure" seems awfully high. Typically a high number of "don’t knows" tends to skew polling result because it suggests a lot of ambivalence in the entire group of those polled. In other words, even the those supporting or opposing opinions are likely to still be up for grabs.

In short, this is still virgin territory and people are more than just a little confused on what to think of it.

I would add that this issue is regional in nature. The further one gets from a border, the more ambivalence they will encounter. Which in turn will skew any broadly based poll.