I'll stop when you stop just clanging the enemy for 15minutes and ignoring the capture that needs to be interrupted.
But scoring headshots above the shoulder of a teammate with a Dire Avenger or BolTac is so fun, getting all muh assists! I mean, i'm not joking, if you are in close quarter, it's fairly doable, I would even argue that it's very important as Tactical/Dire Avenger. The best way to do it is to flank the opposing melee specialist of course to avoid... Accidents. Plasma/Nading into melee.. That's another story.
Sorry, but when i storm into an objective, and i see one of my teammates clanging it out with someone else, i shoot (Mind, mostly i am Bolter-Traitor) after making a half circle around my teammate. Not because i want to score a kill or take yours away, but having that ally free is more worthy than his personal duel with someone. Better get that point captured then watching you batteling it out, sorry I also have to say, i rarely ever shoot my teammates while doing this. 1 Stray Bullet or so can happen, but i rarely down my ally with this
I will continue to flank the melee guys and Kill the one trying to slap my allies, no matter how intense is your melee combat. PS: Not with plasma / Grenade. Just with my Bolter.
Shooting into melee combat is something that is VERY useful and powerful, however it requires teamwork and skill from both the melee combatant ranged weapon user. In my guild Strikeforce Ultra the melee user and ranged users have a strong symbiotic relationship, the melee user provides a physical barrier for the ranged user so he doesnt have to worry about melee enemies instantly wrecking him. and the ranged user provides an edge in combat that turns the tide in nearly all melee fights. The melee user either beats his opponent or he stalls the enemy holding them in place and not moving all over the place. While that user is locked in combat the ranged user lands skilled shots helping to drop the target. If some friendly fire happens we have a apothecary ready to heal up any damage that may happen to them. In offensive combat the melee user rushes the enemies heavy weapon user locking the gunner in melee combat and distracting all the enemies nearby who panic trying to drop the melee user. The ranged users then drop all nearby targets who are busy trying to protect themselves from the melee user. Dont get me wrong, there are lots of randoms who shouldnt shoot into melee because they arent skilled at it and unload an entire clip into your back. But there are also lots of melee users who recklessly throw themselves at the enemy clanging repeatedly and actually body blocking the enemy making the ranged users stand there and wait until the melee user dies. One of my personal pet peeves is when 2-3 melee users try to all attack 1 enemy target at once (and not from different directions) they end up piling up and stunning each other all spamming attacks out of desperation to get a kill. I have a personal policy that if 2 melee users are already fighting an enemy, i just walk away from the situation. Melee pileups and reckless melee users are just as common and frustrating as ranged players who shoot their allies in the back. Just as a final note, I specialize in melee combat and ground assault. So im not biased towards ranged users.
I often asset if the shot is clean. Usually its the melle that jumps in front of my heavy bolter that ends up getting team killed.