There is such a division between the two major political parties here. Many people just agree with their party line on issues without understanding or thinking for themselves. (And yes, this does happen on both sides.)
Others are ideologically opposed to the government doing anything, for they see it as an increase in power/control that the government has over us.
Also, some of those with good insurance now are afraid that they will have worse health care coverage under a government plan.
There is certainly a lot of fear mongering with regards to this issue. Spreading FUD (fear, uncertainty, doubt) is the quickest way to quell a change like this.