as fun as that sounds, don't you get a huge reputation penalty on all factions if you sat bong a single planet?
No, just with the victim and everyone except TT, Dictat, Pirates and Pathers. Besides, the rep only goes down to -100, there's no difference between 3 incinerated planets and 300. Don't stop if you start, until you're done.
and when i do satbomb the planet it doesn't kill it or its inhabitants.
Size 4- planets get destroyed, anything bigger drops a size level.
so how do i get rid of the Hedge(or any faction)? permanently without having to capture every planet they own.
If you want to just stop expeditions, getting rid of planets with military bases is enough. Unfortunately, that includes Chico and Kazeron, so if you can crack that, you have the capacity to wipe everything. Before bombing, strip-raid them of anything valuable - they won't be needing that stability. You'll need a stable source of fuel - having your own production is perfect, Dictat will also do (so, kill them last). Some planets are story-protected (yuck) and cannot be destroyed fully until they are no longer needed for the story. Bomb them anyway, a dozen bombings will cost nothing in terms of fuel but the accumulated instability will decivilize them within a month after the story flag gets dropped. Assuming you are not going for a complete wipe of all humanity, having a stash of AI cores to make amends afterwards is very helpful.
By Ludd I sound so psychotic. Have fun with your warcrimes!