Neville- I definitely understand it. If you rule something is assur, then you can’t give it to someone else even if they think it’s mutar.
I’m just not sure I agree with it. Lifnei iveir is placing a stumbling block in front of a person… convincing them to do something they wouldn’t want to be doing or enabling them to do something they shouldn’t be doing.
For a stam yid, he has the right to follow his rav and posek. Whether the rav or posek will be held accountable if that psak is mistake is not for me to decide, but the stam yid who relies on a legitimate psak by a reliable posek (like R’ Moshe regarding chalav stam or the Rabbonim who allow Heter Mechira) is doing nothing wrong. He doesn’t need to follow your posek, he can and should follow his own posek. So how could it be considered a stumbling block to enable him to do something that he’s allowed to do? Nu, so your Rav says it’s prohibited… but lifnei iver seems to be about the target. It’s not about what’s permissible for you, it’s about what’s permissible for him. And your posek’s ruling isn’t kovea for all of Klal Yisroel.