Is it unethical to cite a paper or book that you have never looked at?
When you cite a source, you are not actually claiming that you have read it.  What you are actually doing is staking your professional reputation on that source containing the information that you claim that it contains.

In most circumstances, of course, this gets instantiated exactly how you would expect: at least one of the authors has personally read the source.  There are, however, certain circumstances in which citation of an unread source is actually appropriate.  Let me give two examples:


The source is cited as a secondary source, e.g., "Feng et al.[17] claim that the species presented in the Necronomicon[18] can be found in Antarctica."  Here is is appropriate to give the bibliographic "pointer" to the secondary source even if you cannot access it yourself.
The source material may be known by a different route than the original publication.  This frequently happens with software tools and standards: for example, you might cite a standard that you are using even if you haven't read the standards document.  Likewise, if I am using a software tool, the authors often point to a particular paper as the preferred appropriate citation for the tool, and I am happy to take their word for it without reading that paper.


There may be many more cases as well.  It all comes down to this: how certain are you that you really know that the document you cite serves the purpose for which you are citing it?