Why is it that when a Democrat violates civil rights he/she is seen as caving into Republicans?

Obama recently said he would try Khalid Sheikh Mohammed in a military court instead of a civil court. The media largely spun it as Obama playing politics and throwing Republicans a bone. The same seems to go for when Democrats start wars, renew the patriot act, etc. When a Republican does it he/she is just evil, when a Democrat does it he/she is caving into Republicans. Why does no one think that a Democrat might do these things because he or she believes in them just as much as the Republican does.