That's definitely one of the series worst episodes. Because, if they can get Kurn secretly adopted by another family, they can do it without erasing his memory.
Kurn's memory was erased because Kurn couldn't live with himself.
(and what did happen to the borg baby?)
whatever Kurn's personal reasons, it was absurd that they chose such a drastic solution when only A FEW YEARS BEFORE Kurn had witnessed Worf lose and then regain his honor, just as he would the second time.