Joseph, you say that loshon hora and dan lechaf zechus only apply to Shomrei Shabbos.
But your own acceptance and spreading of loshon hora is what brands the Kushners as non-Shomrei Shabbos. However, in most respects they could be far more ehrlich and greater shomrei mitzvos than you. Does that mean that people are permitted to spread loshon horo about you?
You are dan lechaf zechus for yourself but not for others. Don’t you have anything to do tshuva for on Yom Kippur?