DovidBT: Many FFB are taught not to say certain things (especially to non-observant yidden) since it will now put the non-observant in a position of “meizid” (intentional) instead of “shohgeig” (inadvertent).
As for non-jews, if you tell them it’s “We do this because it’s a commandment from G-d” they will generally respond “but it doesn’t say that in the Bible”. Do you really need to then get into a discussion abut Torah Shel Ba-peh?