Every rhetorical endeavor must consider its ethical relationships, and web design is no different. The actions (or inactions) taken by web designers often have ethical implications.
Misleading advertising and dishonest writing have been around long before the internet, but the publishing power and functionality of the web creates new opportunities for unethical actions. While text and images can be misleading, the web's funcitonality can provided an added means to exploit a user. When web design conceals its purpose in order to influence its audience, it can venture into unethical terrain. User interface (UI) or user experience (UX) design intentionally used in this way creates dark patterns.
darkpatterns.org lists common unethical design techniques:
Play the video below from 10:04 or watch it on YouTube to view an example of how "dark pattern" design works.
Web designers must create structure and architecture, but at what point does an architecture unethically restrict a user's needs? Websites must have some kind of architecture, but users should be able to move through them as freely as possible to achieve their objectives.
Are you sure you can use that image? Using copyrighted content on your page is often easy and sometimes tempting. But using others' work without their permission is usually unethical (and against the law)! Check the copyright and licenses for the content you want to use, and use the excellent search tools at Flickr and Google Images to find images licensed for reuse.
What if you just show an to your users through a link (instead of saving the image to your server)? This practice, called hot linking is problematic because it uses the host site server's bandwith to populate YOUR website, and it can violate copyright laws if the image is not licensed for reuse. Provide your users a hyperlink to visit the image's full page instead of displaying it the out-of-context on your page.
Who do you include in your audience? Do you exclude anyone? There are ways to make your website more availble to people with disabilities and other underserved groups, such as older people, people with low literacy, people with low bandwith or older technology, or inexperienced users. The Web Accessibility Initiative offers guidelines and tools to help you make your website more accessible.
Some simple ways to improve accessibility: