I heard on one of Rabbi Berel Wein’s history tapes that the very first deviation that the reform movement made was that they dropped saying one of the Yokum Purkim’s on Shabbos after layning. Kuk vos iz aroise gekumen fun stopping to say one Yokur Purkim. Look what became of those people who started out by not saying one Yokum Purkin. Could they ever have, in their wildest imagination, have envisioned where they would end up?
We have a mesorah and even if something is not clearly assur we are not to stray from our mesorah.
I’m sure that Professor Heschel was a good person and a Talmud Chochom but he strayed from our heilige mesorah and thereby he became krum. He probably never intended to go where he went but just having his name associated with the Jewish Theological Seminary, JTS, made him be machsher it. It’s not our job to judge him, that’s between The Rebono Shel Olam and him but we certainly should not be learning from him. Again he was krum even with the best intentions.