Not true. Serfs had rights that varied a lot between societies and over time. Religions mostly teach a value of human life, and Christianity teaches equal value: "when Adam devlved and Eve span who was then the gentleman", or "the first shall be last and the last shall be first" or "it is easier for a rich map to pass through the eye of the needle".
There were all sorts of people in between. Free people who were not serfs. Skilled people who were members of guilds.