These corporations can legally control the content of their sites. They can decide what sites they will link to. This poses a problem regarding access to information on the Internet. Although censorship is not legislated by government, many large portals have anti-pornography rules and will not list sites that obviously promote illegal activities. Pornography is popular enough that people who want it will easily be able to find it.
Illegal activities are another matter.
They are doing this by not recognizing drug keywords. Since keywords are the words you type into the search box, this means that, through this site, you will not be able to access any information about mescaline or magic mushrooms, for example. This means that they are restricting access to sites about the psycho-active substances that shamans use legally in their countries. They are restricting access to sites that are organizing legal political action to change drug laws and they are restricting access to historical information about other cultures where these substances are legal. The sites that promote drug-use, illegal acts, pornography, etc. are still out there on the web.