You are being absolutely facetious Pearlman.
Letting a child play on an iPad instead of having dinner is against the best interests of the child. As a parent that's your basis for insisting they join you, because to do otherwise is to fail your child as a parent, and you have a responsibility to that child.
You are solely arguing from the viewpoint of the father being allowed to do exactly as he wants, to make any decision he wants, without interference or judgement, regardless of the impact on his son.
He has the child 50% of his non-school time. So if this continues he will have half a childhood where he is able to have friends, go to beavers, earn badges and know deep down that he has intrinsic value as a person, and half a childhood where he is just a thing to possess because he can be possessed, but will not be seen, heard or valued.
For all that my ex is an abusive wanker, who had contact completely stopped by the courts for 9 months, he's got a better view than you, and willingly takes the DC to all their events on his weekends.