Tons of reasons why this is a really bad idea, and I'm staunchly against it.
It breaks accessibility.
Its completely unpredictable. Which clicks open new tabs, and which ones don't? How do I know a click won't open a new tab?
Having every click just open in the same tab is predictable, explicit, and is the norm for most of the web (except the annoying sites which open things in new tabs regardless of if we want them to).