There;s probably a lack of sound evidence because there have been no long term studies on it like looking at the impact on a specific lake over a long time period and covering ALL variables. Here are a few links describing some studies. Notice how not all variables are accounted for like tournaments and more fertile vs. non-fertile waters.
http://www.ms-sportsman.com/details.php?id=1451
http://www.bassfan.com/opinion_article/1360/science-and-the-impact-of-bed-fishing#.Vz8Cu_krLbg
But think of it this way. If you're fun fishing, you catch a fish off of a bed and release it right away and it goes back, there's less chance of damaging impact than a tournament where 50 fish are taken off of beds for 7 to 8 hours leaving them wide open to predators. Also consider the number of bass that end up actually making it past the egg stage vs. the number of total eggs laid. Then consider multiple tournaments over the spawn season. The risk at least is pretty obvious.
You could argue for article #1 where it only takes a few bass to populate a body of water but then you also have fishermen that fish beds and simply take the fish home to eat.
While it's inconclusive, I'd rather not take that risk and tournament bed fish. I've done it, but I think it's pretty dumb. 15 boats all pounding beds vs. finding patterns.