The only reason why Dr Smith was not rid of a long time ago in the episodes due to all his sabotage and mischief, (aside from Irwin Allen the producer of the program to decide and keep him) was to portray the genuine compassion the Robinsons have in general for human forgiveness regardless of the violation. And when one thinks about it, whenever there is any moral standards or laws broken there is at least a place for everyone of those violators--on Earth, (ie, penalties, fines, incarceration, etc) but at least they can survive and redeem themselves there. Given that the entire family is remotely millions of miles away from civilization, leaves only to consider that the Robinsons, may have realized resorting Smith only to an all or nothing recourse for his evil deeds, that is to either abandon him in space or tolerate and keep him under scrutiny in order to prevent any more of him putting the Robinsons in jeopardy. It’s hard to comprehend that the Robinsons are always tolerant with him and forgive him, on every scene that follows a mishap of his. To abandon a human being in space with nothing to live on in uncharted areas, would be probably worse than the ultimate capital punishment, since being in space alone would be slow death and solitude without resources of survival. If this drama has transpired all on Earth, Smith would have long since been gone and out of everyone’s hair.