Well the argument is clearly invalid. Slave owners??
But there's a difference between lousy analogies that further debate through clarification and lousy analogies that lead to everyone telling each other fuck you.
I had no intention of offending you, or the poster, and if that is how it was taken, I apologize.
The poster was concerned about potential losses incurred by existing medallion owners if the law changed. The comparison was made to point out that laws are often wrong, sometimes more seriously wrong (as with slavery or genocide), sometimes less wrong, but wrong nonetheless.
Individuals or classes who benefit from bad laws should not get an affirmative right to recover losses incurred when these laws are changed. In the most serious cases like slavery or genocide, they may even be punished ex post facto for following such laws. I'm obviously not advocating that here, only that the law be changed through the democratic process, despite the potential effects on existing medallion owners.
But there's a difference between lousy analogies that further debate through clarification and lousy analogies that lead to everyone telling each other fuck you.