I for one don't agree that the per se legitimacy of something can be questioned just because it might lead to a chain reaction that results in a negative outcome somewhere far down the line of alleged causality.
Operating an automobile can allow for drunk driving can lead to death of innocent bystanders. This does not call into question the per se legitimacy of driving a car. It might, however, call for strict(er) regulation of the activity.
In many cases, the per se legitimacy of something is related to its overall risk/reward to society. Risk from improper use of cars is less than the overall benefit to society of having such transportation options widely available to everyone. On the other hand, one could argue that the overall impact from emissions, infrastructure requirements, and radical recontextualization of the social fabric, taken together, calls into question the per se legitimacy of POVs.
In other cases, the per se legitimacy of something is axiomatic. The right to free speech, for example, is held by many (most? almost all?) to be axiomatically legitimate per se. No amount of bad speech or consequences of bad speech can call into question the per se legitimacy of the right to free speech.
Which brings us back to the question of strict scrutiny, when proposing to regulate things that are axiomatically legitimate, like pornographic expressions.
