One must realize that many of the laws that we follow, like a man wearing a head covering, is completely made up by the Rabbis without any source in the Torah. It is a custom that was accepted by the Jewish people, but was not a command from G-D. Why then do we follow these types of laws without fail?
There are also laws that are stated explicitly in the Torah, like no kindling a fire on Shabbos. These are clear commands directly from G-D that require no interpretation. It is obvious why these commands must be followed, they are from G-D!
A third category of laws are those that are derived from the Torah by the Rabbis. Meaning, they were directly from G-D, but they were oral traditions that G-D told to the Jewish people. A good example of this are the prohibitions on shabbos, namely the majority of the thirty nine melachos (39 Jobs that were done in the temple or mishkan). The Torah says that one can not do melacha, work, on shabbos, but never defines what work it is talking about. The Rabbis tell us that through the oral tradition G-D made known to us what melacha He was speaking of.
These are the three types of halachas that we have: directly from G-D that can be understood straight from the Torah; from G-D that was transmitted orally and the Rabbis tell us the oral tradition; and laws that are completely made up by the Rabbis without any input from G-D.
Everyone who believes the Torah was given by G-D should agree that anything commanded straight in the Torah should be followed because it is the direct words of G-D. Anyone who does not can not reasonably claim that they, either, follow judaism or believe that G-D gave the Torah. That means that on shabbos, anyone who believes G-D gave the Torah and they want to follow Judaism can not light a fire. There is no differentiating betweek any type of actual fire, because G-D says do not kindle a fire. Anyone kindling a fire is not following Judaism, doesn't believe G-D gave the Torah or they realize they are sinning.