First, there have always been back tees, as someone wise wrote in a recent thread.
Second, you need to define with precision what you mean, in terms of percentages. As in, "is having back tees 10% longer than previous back tees a good thing for the game?" This would take a 6500-yard course to 7150, as an example.
Third, if there was land there already, fine.
Fourth, if the nature of the hole was not compromised, fine. After all, if a 240-yard hitter plays the new back tees, he/she may no longer be threatened by the drive-zone bunkers (now unreachable), but will be threatened by having to hit 2 clubs more into the green.
Fifth, as Jim notes, if costs increased due to lack of third, bad for the golfer.