You can always tell the newcomer who has just started creating web pages of their own. They are the one's asking about "no right click" scripts and other means of protecting the content of their web page from would be thieves. These are the people who don't have enough experience of how web browsers work to understand what can and can't be done with web pages.
Firstly, not all browsers permit web pages to interfere with such operating system functionality as the "context menu" or require the browser owner to grant that permission. This means that you can only block your visitor's access to that menu from the right mouse button if that visitor allows you to block their access.
Secondly, most such scripts only block access to that menu from the right mouse button and don't block the access to the menu from the keyboard. On windows keyboards the key between the right Windows key and the right CTRL key is the contextmenu key which will display the same menu as clicking the right mouse button.
Slightly more knowledgable web page writers move on to encryption as being the way that they use to attempt to protect their web pages. These people may use free programs or can pay anything up to $200 or more for a program that will encrypt their page source. This results in anyone who views the delivered source of the web page seeing only the encrypted version of the page source.
The easiest way to be able to view the decrypted source of an encrypted web page is to install a "View Source" bookmarklet into your browser that will pop up a new window containing the decrypted source of the page that it is run against. There are two ways that the encryption programs can block this - they can block popups or they can use an empty iframe - I have found only two encryption programs that include the code to block this and one uses one of these methhods while the other uses the other method. No other encryption programs that I have seen block this method of accessing the decrypted source.
Given that this last method gives access to the unencrypted source of any web page no matter how encrypted we can therefore conclude that there is no effective way of blocking peoples access to the readable source of your page.