Universal Laws of Nature

Kant posits that a guideline for moral imperatives of duty is to imagine as though your actions would produce universal laws of nature. If your actions would produce non-contradictory laws of nature, you're fine with respect to your duties. If your actions, when extrapolated to all of nature, produce self-contradictory situations, they ain't dutiful. Kant offers a few examples, the first of which states that a person considering suicide for the reason that any further protraction of it promises more ill than good ought not to commit suicide, as following this universal law would cause a contradictory state in which the same impulse that encouraged the advancement of life may also situationally encourage life to end itself. This outcome to me does not seem in itself contradictory. If the impulse produces two different outcomes given two different situations, or an outcome which contradicted itself, I would say that was an untenable law. But Kant's objection seems to be that the law is untenable because it could produce two different outcomes (advance or destroy life) in two different situations (life promises more good than ill; life promises more ill than good). Barring a misinterpretation of Kant's example, I do not see how this is in itself contradictory. To state it another way, Kant's objection is that if the impulse which compels life is pleasure, that same impulse cannot also compel the destruction of life. But it seems to me that if the reason we live is for the sake of pleasure, then lacking a positive outlook on pleasure it is perfectly rational to end one's life. The law does not appear to be contradictory to me.