As someone that occasionally does this, I'll clarify a few misconceptions.
1) You don't need to do the landing pad "exploit" (if you want to call landing an exploit, fine w/e). A Viper fitted with 4 Size 1 Dumbfires, two B2 shield cells (to tank internal station guns for ~50 seconds), and all E mods costs ~10,000 Credits or less to replace which, humorously enough, is often less than the cost of an ammo reload. So it may be cheaper in fact to kill someone and then let the station kill you then to reload. \o/ for Easy mode re-buy feature.
If you want to go even cheaper, an eagle can fit 3 dumbfires and costs 5000 credits to replace - and it will respawn fully loaded at less than the cost of a full magazine of dumbfires. Re-buy is a hell of a thing.
2) No one uses the "point defense" bug. I've killed Pythons, Type 9s, Type 6's, Asps, clippers, and Cobras with sustained, direct dumbfire hits. The only ship to survive the attack was an Anaconda about an hour ago. Took him down from full shields to 38% Hull in seconds, he combat logged. Though I imagine the PvP=Grief crowd will rush to defend his use of that "exploit." Either way, he had a nice repair bill waiting for him.
3) As to the "Why?" of the thing, to take a break and unwind. I was trading in my Type 7 today in Beta Sculptoris, trade grinding for, amongst other things, a fully kitted out exploration Asp to see the galaxy. After hours and hours of trading I decided I needed a break. Well, this being a video game (emphasis mine), I decided to shoot some folk. This being a first person game, with shooty mechanics and multiplayer, I thought it would be fitting.
I would've done the whole interdiction thing, but every person I've ever interdicted to try to "legit" pirate for cargo has combat logged. Go figure. Well, you can't combat log fast enough inside a station with wave after wave of dumbfires heading your way. Heh.
I have to admit, this is the first multiplayer game I've played where simply shooting someone is called "griefing" and "murder". This community is an interesting bunch, that's for sure.