Here's an interesting one

urchase Contraceptives Online
Result: sponsored ads.
What's the problem? All contraceptives are illegal in Spain. Remember, the www in
www.google.com stands for
World
Wide web. Google is now enticing their Spanish users to purchase something which is illegal.
How about: pseudoephedrine hydrochloride
Result: sponsored ads.
What's the problem? Pseudoephedrine Hydrochloride is a popular over-the-counter nasal decongestant. It's the generic name for Sudafed. BUT, it's also a key ingredient to make methamphetamine, meth. To cook up a big batch of meth, I need a big bunch of pseudoephedrine hydrochloride pills. So, most retail stores limit the amount of pseudoephedrine hydrochloride products that a customer may purchase and most instruct their clerks to be on the lookout for persons buying excessive amounts. It's not hard to find a judge who will grant a search warrant based only an an unusual pattern of pseudoephedrine hydrochloride purchases. Buying it online would be the perfect way to dodge those safe-guards. Many US cities have actually passed ordinances restricting the quantity of Pseudoephedrine Hydrochloride that can be sold to one customer at one time. How can google be sure that their advertizers are going to comply with all of these various laws?
Hmmm.... while they help meth cooks, I'm glad that google is keeping us safe from evil knives....
How about: Satanic Literature
Result: sponsored ads.
What's the problem? I was just reading the other day about an American city, I'm sorry that I can't remember the name, that has illegalized satanism and its trappings. It's a city ordinance. Of course, this city ordinance will not stand up in court for even one minute. The ACLU is already challenging it. But, for the moment, it is a standing, valid law and google is now advertising material that is illegal in at least one city in the US. Can google keep up with ALL of these laws of every city and every state much less every country?
Let's try one more: Art supplies.
Result: sponsored ads.
I looked at one of the sponsored ad sites and found that they sell permanent marker pens, printing ink, and spray paint.
What the problem? Many American cities restrict the sales of these items to minors in an attempt to curb graffiti and vandalism. One could argue that by taking these ads, google is helping these vandals find the supplies they need.
What, I ask you, is the difference between an art supply site that, among other things, sells spray paint, marker pens, and printing ink which are restricted in many jurisdictions in the US, and a cutlery site that happens to sell, among other things, balisong knives?
You might say, "The difference is the intent. Spray paint, while it might have criminal uses, is really sold as an art supply for artists to create art works with. Butterfly knives are just evil."
But I'll bet you a month's salary that more crimes are committed every day with spray paint that have been committed with balisong knives in the last twenty five years.
I am a balisong artist. For me, a balisong is a form of art supply. To someone who is a vandal, spray paint is a tool of crime.
As has been pointed out in this thread, everything is illegal somewhere. By accepting an ad for a knife, google is not forcing its users to buy that knife. The buyer is the one who puts out the money and makes the purchase. The seller is the one who ships the product. It is a transaction between buyer and seller and it is the responsibility of the buyer and the seller to assure that they are complying with applicable laws.
I heard just the other day that there are some 36,000 jurisdictions in the US. 36,000 sets of laws, and that's just in America.
Furthermore, the fact that I did a search for contraceptives does not mean that I'm interested in purchasing any. The fact that I did a search for pseudoephedrine hydrochloride does not mean that I'm planning to make meth. The fact that google provides search results including sponsored links only means that google is doing the task they set out to do: to provide information. What the user does with that information is the
user's responsibility. It's very much like those pseudoephedrine hydrochloride pills. You can take them to relieve your cold, or you can make them into meth. That's
your responsibility.