The anecdote about the strict earthly father actually illustrates the problem perfectly. Jesus himself anticipated exactly this objection: "Which of you fathers, if your son asks for a fish, will give him a snake instead?" (Luke 11:11). He invokes ordinary fatherhood to argue that even evil men know how to give good things to their children (Luke 11:13), and then contrasts that with the Heavenly Father who surpasses them all, being "kind to the ungrateful and the wicked" (Luke 6:35).
The tough-love father who kicks his kid out with two months notice is precisely the kind of flawed, conditional fatherhood Jesus uses as a floor, not a ceiling "if you, who are evil, know how to give good gifts..." The Good Father exceeds even the decent ones.
And here's the contrast Jesus draws implicitly: the Hebrews complained about their food and longed for the fish they had in Egypt (Num 11:5). They were, in effect, children asking for a fish. And what did YHWH give them? Fiery serpents that killed many of them (Num 21:6).
Jesus asks what father would give a serpent to a child asking for a fish. Yahweh literally did. The distinction isn't special pleading, it's Jesus's own logic carried to its conclusion.
