Linking of Web sites to one another is extremely common and is, arguably, both the raison d'etre of the WWW and the reason for its success. It is custom and practice, and so if a copyright owner puts up a Web site, he MUST expect others to link into his site. Services such as Web search engines could not operate without this ability. When someone opens a shop, they expect people to walk into the shop. Customers do not have to get permission from the shop owner, to go inside, even though they are entering private property.
Permission is inferred, by the presence of the shop, and that the door is unlocked.
This is how most shops operate by custom and practice. If you don't wish people to walk into your open shop, you should clearly state that fact, at the shop's entrance. In fact, Web sites are shops. Find out how.