The fact remains that in todays fast environment "see and avoid" can only be described as inadequate as the sole method of avoiding collisions. Yes, we all know that we should keep a good lookout, but there are a lot of things we should be doing at the same time and often in a cockpit that was not designed to give us the view required to maintain a decent lookout.
So I agree that if even only in the interest of self preservation, our glider friends should make an effort in making themselves conspicuous and avoiding areas where other traffic can pose a significant risk. It's not about "having the right" to be there, but whether it is smart to be there. After all, being right does not mean a thing when you hit the ground in pieces after a mid-air..