Putting _blank on internal links is a pretty unnecessary (and horrible) thing to do in my opinion
The blank tag was made to keep people on a site, not for forcing them to keep track of x amount of tabs or new windows.
Remember that most people probably won't be
reading TLS as they read a book (before page 4 you must have read page 3), they will be
browsing it. They'll look at an article, go nah not interesting, then click on the next thing they find interesting, and probably they'll do it quite fast as well.
The problem is, one way of doing this leaves some control up to the user, the other gives them no control at all. I can't imagine what I'd do if sites like say Wikipedia forced me to open a new tab for every link, I would end up having 50 tabs open which I wouldn't be able to keep track of anyway, plus I'd be super frustrated about having to constantly close tabs.
Edit: Sorry if my tone is very rude and direct in this post, it was not meant to sound that way; been writing too much Norwegian today X)