Spinoza and Kant on reason and universalizability

Spinoza writes (Ethics, Scholium to 4P72):

The question may be asked: "What if a man could by deception free himself from imminent danger of death?  Would not consideration for the preservation of his own being be decisive in persuading him to deceive?"  I reply in the same way, that if reason urges this, it does so for all men;  and thus reason urges men in general to join forces and to have common laws only with deceitful intention;  that is, in effect, to have no laws in common at all, which is absurd.

This not only agrees exactly with Kant's position that lying is always wrong, but the form of reasoning is rather Kantian.  So the first form of the Categorical Imperative precedes Kant not just in doctrine but also in rationale: if reason tells me to do something, it tells everyone this.

And, while I agree the conclusion that lying is always wrong is correct, Spinoza's version of the reasoning just doesn't work.  For defender of lying to save innocent life does not say that reason says that one ought always deceive or even that one ought deceive whenever it is to one's advantage, but the claim is more narrow, say that one should lie to unjust aggressors in order to protect their victims.  And the universalization of this narrow claim does not lead to the sort of absurd social situation Spinoza points out, though it leads to the kind of contradiction that Kant is worried about: if everyone lied to unjust aggressors when this would save lives, unjust aggressors wouldn't believe the claims of those who speak to them, and there would be no point to the lie.

That said, I am in general kind of dubious of universalization arguments.  There is, after all, the classic example of playing tennis Saturday night because the courts are free.