I'm sure I'll be corrected, (and if so, I welcome it, but bear in mind that there are multiple authors with multiple explanations of how this tech works, so I'm not sure there is a 100% right answer) but my understanding of how phasers work is that they can be set to a frequency and intensity that disrupts neural activity temporarily (stun), another that does so permanently (kill), and yet another that can heat by exciting molecular activity (heat), and yet another that can do that to the extent of breaking an item's molecular bonds altogether. Given that description of how they work (or any other you care to offer, because I believe this will probably still hold), how are they *not* increasing incidence of cancer, even on light stun? Maybe they do, and for the major galactic civilizations this is just something that the medical staff quietly takes care of on a regular basis? If so, what does that mean ethically when our hero crews go merrily waving their cancer wands at native "primitives" while on away team missions?
Given how frequently people just shrug off getting shot by a phaser in Trek, I'd say old fashioned guns are more deadly.
The alternative is to use plastic bats to ward off adversaries for fear of hurting them. A phaser is a weapon, a defensive one that can also be used as a tool for cutting things, but a weapon all the same.
Presumably, whatever cancer risk a phaser poses is negated by the fact that cancer is curable in Trek's time. As for primitive civilizations exposed to phaser fire, perhaps an undercover medical team stays behind to cure anyone infected clandestinely?
There's probably a higher risk of getting cancer from drinking too much water rather than low yield phaser stuns.
I'm not sure what the conceptual link is between "disrupting neural activity" and "increasing cancer risk." Cancer results from genetic mutations, such as those induced by ionizing radiation. We don't know if a phaser stun is intense enough radiation to be ionizing. Presumably the "heat" setting is akin to microwave or infrared radiation, too low in energy to cause mutations. The stun setting would likely operate at fairly low frequencies of the sort that have been conjectured as having some effect on human neural activity. Despite what cell-phone fearmongers may claim, there's no scientific basis for the idea that microwave or radio emissions can have a carcinogenic effect; that should be a physical impossibility, since such wavelengths are simply too large and low in energy to penetrate DNA molecules and knock out particles. (It's akin to the difference between being hit by a bullet and being hit by a weather balloon.) Anyway, people who travel in space for a living would be exposed to a lot more radiation as a matter of course than us Earthbound types. The occasional phaser stun would probably be a drop in the bucket where their annual exposure levels are concerned. And what about transporter radiation? That stuff's intense enough to disintegrate your whole body. If they're not worried about that, then I doubt phaser stuns would trouble them much.
This wholeX is not safe at any level phrase troubles me. With trans-fat--if you excercise--it is okay in small amounts. The anti-nukes talk about how no level of radiation is safe. How do you think evolution happens? Brownian motion has a role in biology: http://en.wikipedia.org/wiki/Narrow_escape_problem I think people are a bit too fearful of radiation.
No matter the output of the stun blast, if you find yourself getting stunned so often that you develop cancer, you'll probably want to change your tactics.