I have a very good reason for wanting to set the default to open in a new tab.
I am currently going through a facebook forum to save every post and have to click hundreds of links of "See previous comments", "See more comments", "See more" and so on to get all the content of all posts.
Those links merely add to the data.
It is virtually impossible NOT to occasionally click on someone's name and then all the effort to date is lost and one has to start all over again.
Removal of this option is VERY annoying and it is a reason for me to find and switch to a browser that does have such an option.
I'm sure there are lots of other people who don't want to lose the page they are on when they click on a link - it can be most annoying to lose the current page.