It is voluntarily ridiculously extreme, because the parent comment was itself ridiculously categorical.
The thing is: most of the time, retro-active laws are dangerous tools that should be used rarely and with caution, but sometimes and when some people have been doing something that they knew was evil even though not technically illegal, it can make sense to punish them with laws designed after the fact.
That’s one line everyone remembers snipped from somewhat more nuanced context.
Knuth said: "Programmers waste enormous amounts of time thinking about, or worrying about, the speed of noncritical parts of their programs, and these attempts at efficiency actually have a strong negative impact when debugging and maintenance are considered. We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. Yet we should not pass up our opportunities in that critical 3%."
Also, it is morally different when you want to punish lawmakers.