For those who violate Shabbos we try to bring them around to fully keep Shabbos. We generally assume that they were not fully aware of seriousness of the violation. When I learned the Gemara of Shabbos I learned that one who violates Shabbos, but does not know the seriousness of the violation can later bring a sin offering to atone.
To bring them to fully keep Shabbos we must show them the beauty of Shabbos, not invoke “Fire and Brimstone” which can turn them off and lead then to fully give up trying to keep any of the Torah.
For those who violate the 6th commandment, we are more interested in protecting society, than in trying to “bring them around”.