I agree about the manual headlights. The setting on this Honda means I won't need to resort to them in the rain. The warning chime is useful when they need to be used. The reason I don't like that option is that they go off automatically, even in the manual mode, on my other cars, so it is confusing.
I understand what you are saying about the law. Many people would think your "if/then" argument would carry the day, but I can assure you that you'd be fighting an extremely uphill battle. The undeniable fact is that laws are constantly interpreted as to meaning and intent. Attorneys frequently find themselves in the position of having to explain to clients that the client' interpretations of what a law means are not, in fact, how the laws are interpreted and applied. Were it a ticket, you would go into court and the officer would say that he had his own wipers on, that it was raining, that other cars had their wipers on, and the judge would be uninterested in your argument.
One thing you can rest assured of is that if it came down to an accident, especially a serious one, you would be in a very unenviable position trying to argue that your windshield treatment did away with the need for wiper usage, and that therefor you also didn't need to turn your headlights on. You might be able to prove that the use of the wipers was unnecessary due to the treatment, but good luck with arguing that that meant you didn't have a legal duty to turn your headlights on. The reasonable person standard would definitely come into play in a situation like that, and your actions would almost certainly be adjudged unreasonable by a jury or judge. I may not be able to convince you this is true, but I know for a fact it is.