If someone were transgressing secular laws, e.g. committing murder or robbery, would a tolerant attitude toward them be acceptable? Why should we more lenient with halachic transgressors?
Hashem always accepts Tshuva, People not so much. If you break shabbos and really do Tshuva Hashem will forgive you, however if you kill someone you really cannot do tshuva for what you did, the people might never forgive you and you cant undo the damage you did