I think he didn't want his family to be ripped apart and thought he was providing them with a merciful death or some shit like that. And yeah, his son acted irrational, but then again some people in real life are pretty damn irrational, to say the least. There's a difference between characters acting dumb in an authentic way and stupid decisions being forced upon those that aren't prone to make them. Personally I don't think this show reached the WD faulty logic level yet, but I do fully expect it to happen in the future.
Shout by MarthBlockedParentSpoilers2016-04-18T20:30:08Z
Father fixes the fence just to kill his family later. And his son makes a very irrational decision. Jup, TWD logic is back. Just waiting for the return of the ninja zombies now.