Praying together has scriptural backing. Further, what is in the heart when anyone prays? Are you working under the assumption that no prayer to God has a selfish motive? "The heart is deceitful, who can understand it?"
That being the case, your argument should be that no one should pray at all. Praying together is no worse--and no better--than praying alone. Either can also be right and beautiful, when done with love.
When the house sold, was it an upside down statue, or the prayer? Prayers can still be answered despite a grin and a shake of the head at the desperation of man.