The Commandment of Shevut: How Do We Handle its Inherent Subjectivity?

In Deuteronomy, we are commanded to keep Shabbat as restfulness.  Many are unaware that this does not just involve practicing the Shabbat observances and restrictions --Biblical and Rabbinic-- but the highly unusual special-to-itself halakhic category of "Shevut," usually translated as proactively keeping "the spirit of Shabbat."  The category of observing "the spirit of Shabbat" is inherently subjective, and it can vary from person to person.  For one person, reading a newspaper on Shabbat is a violation of the spirit of Shabbat, while for another it enhances the spirit of Shabbat.  Going someplace for Shabbat dinner or lunch might enhance the spirit for one, but for another take away from the Shabbat spirit of the sanctuary of home.  The issue has come to the fore with the electric car.  Since an EV has no fire within in, and electricity meets none of the halakhic prohibitions, its use on Shabbat largely comes down the category of shevut.  This has produces two approved Responsa of the Conservative Movement, which are largely hostile to one another.  In one, anybody considering the use of an EV on Shabbat should be considered in violation of the law, and shevut should not be considered subjective, but actually somehow defined by a small group of rabbinic authorities others in perpetuity!  (It's like saying, How dare you read your psychology textbook on Shabbat!  That's homework!  Even though you are allowed to read on Shabbat and you love psychology.)  The other group decries this attempt to take over and monopolize our one subjective category.  I explore the issues.