Alas, he often gets cited by people who have no idea what they are talking about. Two cases in point. Patrick Appel, writing on Andrew Sullivan's blog, points to some guy named Ben Canoscha, who says:
In Kant's Categorical Imperative he includes this moral maxim of universality: "Act only according to that maxim whereby you can at the same time will that it should become a universal law without contradiction." In other words, if your action were to be the action everyone was taking, would you still do it? The implications of Kant to non-voters would be, "If everyone chose not to vote, the democracy wouldn't function. So vote!"
That seems like a fine aspirational ethic -- a principled stance applied to things like democracy and drug buying -- but the more realistic approach would to weigh the probability of universal adoption of the action. If it's insanely low -- like in the case of non-voting or drug-buying -- then ignore it. If, on the other hand, there were only five total drug buyers in the world, and if you stopped buying drugs that would drastically shrink demand and perhaps result in less drug violence, you would be right to incorporate societal implications more seriously in your decision as they much greater.
Bottom Line: In the case of buying drugs, since the personal impact (positive and negative) so vastly outweighs the societal impact, I believe solely a personal consideration of costs and benefits is an ethical way to think about it. But ethics is simply a basis for making individual decisions, and to each his own. (Italics mine)
Really? To each his own? So it's like totally okay for me to molest a child? And an SS officer is just as good a person as Gandhi? Because, you know, to each his own. But I digress. Anyhow, Appel replies:
No one would argue that this pedophile should "weigh the probability of universal adoption" before making the decision not use child pornography. Kant's maxim only works well when debating the direct effects of an action.
To both bloggers: Kant's ethical theory is most definitely not about weighing the consequences (or effects) of an action. So, contra Canoscha, Kant's ethical view cannot be summed up as: "If your action were to be the action everyone was taking, would you still do it?" Applying Kant's theory depending on the consequences of an action is not using his theory at all. To Kant, acts are right or wrong in their nature, not because of the consequences of the acts. Mr. Canoscha is obviously a consequentialist (although, oddly and perhaps inconsistently, also a subjective relativist). That has its own problems, but if you believe that what matters morally are the consequences, why even bring up Kant at all?
Also, please note that Kant's not saying that any action one performs should be good to go for a universal law. I can permissibly go to the gym at 3:30 today, even if it doesn't make sense that everyone go to the gym. What Kant says is: "Act only according to that maxim whereby you can at the same time will that it should become a universal law without contradiction." (Italics mine). What matters is the maxim by which one acts.
Acting by the Categorical Imperative is not supposed to be a matter of weighing two possible worlds, and picking the better one. Again, it's not about consequences for Kant. It's a matter of logic - if the maxim even makes sense as a universal maxim. For example: lying. Let's say I lie under the maxim that I must say whatever it takes to get me out of a rough situation. But if everyone could act on that maxim, then promises would mean absolutely nothing - and lying would not even be a rational act to to perform. So promises would not exist, and a maxim saying you could break a promise could not exist. Therefore, it's irrational.
There are five formulations of Kant's Categorical Imperative. Most philosophers do not think this (that is, the universal law formulation) is the best one. Might I suggest the humanity formulation?
PS. For the record, I think it obvious that using child pornography (or perhaps any pornography) is treating someone as a mere means. It is arguable whether Kant would think drug use is treating oneself as a mere means.