Well...warp drive, due to the entry into subspace, I personally see as more dangerous to the ship than the planet--the gravimetric shear would tear the ship apart if you weren't careful. (Which is why I consider Berat's stunt at Septimus III one of his List of Moving Violations.
For impulse...I see it as partly related to an ion drive. We HAVE seen an instance where such a drive was inadvertently weaponized (Star Trek IV). However, what I'm seeing is an effect more like a lot of lightning. It charges the atmosphere around it, and when that electricity discharges, you get a lot of lightning strikes. Do that in an inhabited area, or a heavily forested area, and you've just succeeded in starting a damn big forest fire. Or do it in a city and the effect could make it look like an area got firebombed. There is also the possibility of power grid and weather disruptions...not on the order of the Probe, by any means, but on a planet that's more atmospherically active than what I imagine Lessek to be, I think there's the chance of creating a storm (not a huge one, but possible...hell, even a big enough forest fire can create a lightning-generating storm).
So basically, the maneuver is banned partly because of property damage (power disruptions, infrastructure disruption), partly because of ecosystem damage (forest fires, etc.), and partly because of the threat to any life that happens to get caught in any of these conditions.
Not to mention the threat to air traffic in the area (which you saw with that shuttle that took one of the lightning strikes).
THAT SAID...as I said at the top of this segment, I made a decision to only go so far with the science, and I'm aware it may not hold on closer examination...you do have legitimate opinions and I probably did some stuff that may either be flat-out wrong, or impossible. As a writer, I am more interested in dedicating my detail work to the character, culture, and linguistic aspects...so I can live with that.
Thanks for reading, guys!