Public Defender won't file a motion to dismiss

Not knowing anything about your case, your public defender probably will not file a motion to dismiss because they believe that there is no basis evidentiary wise to support such a fiing.  If you believe evidence was obtained illegally, i.e., without a warrant for instance, then talk to them about that. There are times that a plea bargain can be in your best interests.  If you want to contest your case factually or based on the evidence, then your public defender is right--a jury trial could be a way to resolve your case if you feel that strong about your innocense. I encourage you to talk to your lawyer about your frustrations regarding your case.  I'm confident they will be able to explain it to you to your satisfaction.