Well...I didn't read every reply to this, but I think that Carl has a similar position to mine. I'll make this pretty short and sweet, so here goes...
You mentioned that herpers don't present a threat to habitat. I have to entirely disagree with this statement. As Carl already pointed out, by rolling logs and flipping rocks, you are breaking a seal that holds in the moisture that the very animals you are selecting for. It often takes a while for this seal to be reformed, and with more and more research showing just how territorial even the little redback salamanders are, this can present a problem if you even flip a log and render that spot useless to that particular animal, which (I am going on a limb here) might make them more vulnerable to predators as they seek out another suitable microhabitat.
Another good example is people who might be searching for aquatic animals (and thank God I'm not included in this mass). Many people while dipnetting frequently throw piles of leaves they scoop up onto the shore and sort through it to find the object of their search. While this may seem harmless, you are destroying the habitat of the particular animal you are looking for, as that leaf litter not only provides a source of protection from predators and an important microhabitat, but it also provides the base for microorganisms which ultimately end up feeding even the animals highest up on a food chance. I have MANY times visited vernal pools, small creeks, etc that have literally piles of leaves on the banks from people searching for fish, salamanders, inverts, etc. Basically, its just a smaller form of dredging, and we should know how detrimental that can be to an area.
Another example that I have to bring up is in reference to a couple of papers I have read, and unfortunately their citations elude me at the moment, but if I find them I will definitely put them here for everyone to read. One of the papers provides evidence that human interference in even remote areas can actually indirectly harm the animals you search for. Apparently predators and foragers (raccoons, opossums, mink, and I believe even snakes were included as predators), can detect where people have disturbed a log or rock (it may be due to human pheromones), and will routinely search beneath these items for prey. It's early and I'm lacking in sleep, so I'll put this in terms I can understand: basically, you go searching for a salamander or snake, you flip a rock..Surprise! salamander/snake. Few hours later, another snake, raccoon, etc detects the disturbance, looks under your log, and eats the critter you were admiring a few hours ago.
One last example I am going to bring up, while this may/may not directly affect the herps, but based on quite a bit of experience with other people, most herpers don't seem to be too conscientious of the local flora in an area. I always cringe when I am out with someone and they are just smashing ferns or worse, trilliums, Arisaema, bloodroot, or other spring ephemerals that are incredibly dependent on their temporary foliage to aid in building up carbohydrates that will be used the next year. There is another study that I have read (again, the citation eludes me) that showed that when trilliums (which generally only have one stalk per tuber) are broken (say, by a herper trodding through some woods) or eaten, they fail to bloom in successive years due to the lack of ability to store energy from their lost foliage. It just seems a shame to me that an area that is beautiful for more than just the herps isn't recognized for one, and further the plants suffer the consequences from the mere walking of (pardon my wording) thoughtless herpers.
Okay, I'm going to stop there because I think my brained my damage from all this writing after a calc midterm and inbetween studying for a chemistry exam...
So much for short and sweet, eh?
~Mike