2) He deprives the Faithful Departed of needed prayers, we may now all assume they are in Heaven, based on Father’s homily, and so we need not worry about (pray for) them.
3) He harms himself by doing the above.
Misleading the Faithful. Father is certainly correct that there many saints in Heaven whose names we do not know. But we cannot assume that our loved ones are in Heaven just because believing so makes us feel better. And we must not assume that getting to Heaven will also be easy for us. The Saints with an “s-t” in front of their names went through some heavy trials. The souls who have reached Heaven have certainly undergone a purging that we on earth cannot even imagine. And just thinking happy thoughts will not change that for them or for us.
Harm to the Faithful Departed. Perhaps some day, these priests who make every funeral Mass into a canonization ceremony will get a clue. If the deceased is already in Heaven, why would we pray for him or her? Isn’t the intention of a funeral Mass to pray for the deceased person – at least in part? And if the person is already in Heaven, why would we continue to pray for the repose of his or her soul? Why should we bother to offer Masses for the deceased? Puh-lease! We should not assume that our deceased loved ones are in Heaven; rather we should continue to pray for them as if they were in purgatory! The graces will not be lost, even if they have gone to Heaven. Our Blessed Mother will apply the merits to some other soul in need.
Harm to the Priest. The priest is responsible for the souls of those in his parish. If he misleads them, he is derelict in his duty. And if he is derelict in his duty, his soul suffers. The parish priest has much more to answer for than do his parishioners. They count on him for guidance, and if he leads them astray…well, what does the Gospel say about that? “Whoever causes one of these little ones who believe in me to sin, it would be better for him to have a great millstone hung around his neck and to be drowned in the depths of the sea” (Matthew 18:6). By preaching as he did today, Father was shooting himself in the foot.He probably believes that “All Dogs Go to Heaven”, too.