Search providers like google don't just show you links though. They also show you potentially relevant excerpts so you often don't even need to go to the linked site to get what you were after, and show previews of images in image search etc.

Determining exactly where to draw the line of what to consider fair-use for things like this is a highly complex and dynamic issue. Web search engines are (by necessity) parasitic as well but that alone neither makes them bad nor illegal.

Parasitic is also not the "bad" counterpart of symbiotic. A symbiotic relationship is simply a parasitic relationship that benefits both parties. Just saying parasitic says nothing about which side(s) would benefit. I think exploitative would be a more appropriate word to use for such relationships.