No. To be in violation of copyright protection, you generally must be *making use *of the material, usually in a commercial manner.
“Mortal sin” cannot be applied categorically to copyright infringement, even if it is deliberate and knowing. If you copied say, a book that was beginning to be a commercial success, and reprinted it abroad for sale to millions without paying the author or publisher, that would be grave matter. But copyright infringement has a myriad of possible instances which may be minor or no infringement at all.
Breaking copyright law might be sinful, but looking at the website is probably not in and of itself breaking copyright (of course it depends on the country you are in).
In the United States, copyright does not equal absolute control over published material. Just because an author doesn’t want a work used in a particular way, doesn’t necessarily mean it is a violation of copyright to use it that way. For example, small excerpts for the purpose of review or for education are allowed. Likewise, lending a legal copy of a book or movie to a friend is also allowed.
In general, my guess would be, in the above example, that copyright violation (if any) is on the part of the poster of the material, not the viewer. The viewer would only violate copyright if they downloaded the work.