Can all the links be defaultively opened in a new window?
It is very inconvenient when sources are listed to ping back and forth.
There's an important usability problem with that: you remove user control. You can open a link in a new window (or new tab) right now, by clicking the scroll wheel on your mouse, using the right-click menu on your mouse, or long-pressing on your touch device. So today you can either load the page in the current tab or launch a new one. If you make "launch new window (tab)" the default, though, there's no way for somebody who wants to load it in the current tab to do so.
Sites that impose the launch-new-tab pattern on users tend to produce lots of tab clutter, and sometimes I don't even notice it until later because the browser switches to the new tab. I notice when I'm done, want to go back, and find that the "back" button doesn't work, and then I have to dig around to find the original tab.
Besides, you don't want this for every link; using the front page would rapidly become unusable. So maybe you're only asking about links from within posts -- which links? External ones only? Comments too? What about links in close reasons (which usually go to meta or help)? Community bulletin? Ads? Inbox? Do you see how this could lead to a lot of confusion about what behavior to expect before clicking?