A Smaller Sin Than the Next One
In Minchas Shlomo he permitted serving a guest who would be offended by being asked to wash, because refusing could lead him to something worse.
In his responsa Minchas Shlomo, in the discussion of placing a stumbling block before the blind, Rav Shlomo Zalman considered what happens when a mitzvah is weighed against its long-range effects. His example was a non-observant guest who would be upset if his host asked him to wash his hands and recite the blessing before eating. The Rav permitted serving him food and drink. The reasoning was that turning him away would lead him to a graver future sin, while the sin of serving him was smaller than the one anticipated. So serving him did not count as causing him to stumble. The ruling shows a mind that looked beyond the single moment to the whole person, and a heart that preferred to keep a Jew close and gently connected.
Source: Minchas Shlomo, chapter 35, as cited in Jewish Action, "Gentle Giant"
When you are tempted to correct someone who is far from observance, ask first what your correction will lead to next. A comment that feels righteous today may close the relationship for good. This week, choose one person you could welcome without conditions, a neighbor, a coworker or a cousin, and offer simple hospitality with no lecture. Closeness built patiently often does more good than any single argument.