As noted by @Robev Rav Hershel Schachter quotes the Rav in his Nefesh HaRav page 230 that it was an issur gamor (complete prohibition) to watch the Kennedy service that took place in a church and was broadcasted on TV. He expressed, what is the difference between going into such a place or bringing that place into your home?
I heard in a shiur (8:10) from Rav Aryeh Lebowitz in the name of his Rebbeim that Rav Soloveitchik was furious that frum Jews watched the funeral of President Kennedy, which was a Christian service in a church. He felt viewing the service was an act of participating in it.
The Rambam quotes this view (Teshuvot Harambam ed. Mekitsei Nirdamim 369). He doesn't name the source of the view, and he himself doesn't support or reject the fact itself.
ואם יאמר אדם שהבית שהם מקלסין אותו בית ע"ז הוא וע"ז צפונה בתוכו שהיו עובדין אותה אבותיהם מה בכך. אלו המשתחוים כנגדו היום אין לבם אלא לשמים
If someone were to say that the house ...