Maybe with : "You're right it is, it is about as disrespectful as telling someone else how to play".

I absolutely loved leveling as BM. It was great fun.. I still love switching to a bm spec and tanking heroics.

That having been said your random heroic isn't all about you (or me, or any individual in it). Everyone's purpose in a pug run (with friends who don't care it really doesn't matter) should be to get the place done as smoothly (with or without getting through the place in less than 15 minutes) and efficiently as possible.

BM just doesn't do as much good for the "team" as MM or survival does (and yes in this instance I am mostly but not solely referring to dps numbers). Not all other players (truly from what I've seen very few other players) will be happy accepting said handicap.

Me I don't care. I'll take friendly, or well, not stupid any day over 5k gearscore and lippy.

I occasionally run heroics in my BM spec to have more time having my spirit beast out. Never gotten any crap for it. Of course, if I did, I'd probably ignore it, out-DPS the jerk, then mock him by telling him "It's disrespectful to the group to doing less DPS then the 'lowly' BM hunter."

Honestly, there's nothing wrong with BM for heroics. Especially since most groups greatly out-gear them anyway. If someone's going to be nit-picky over something so ridiculous, then they ought to only do fully pre-made randoms.

I don't run in BM for heroics but I'd hardly call it disrespectful when you sure as shit don't need the BEST dps for a heroic anyway. It's going to go just as smooth with a BM spec if you know how to play as it would with Surv or MM, honestly. The difference in DPS is dramatically less when you're doing something like a heroic.

BM brings FI procs and a strong pet who can interrupt once in a while. There's alot to a BM hunter that people don't really see. Sometimes my pet is the only thing between us and a wipe when the tank goes down. In terms of usefulness, I'd say MM > BM > SV as far as group buffs.

Honestly, just ignore them and prove them wrong by doing the awesome DPS that you do. Those type of people have no idea what they are talking about. How is it disrespectful to the group? DPS is your job and that is what you are doing.
The only way it would be disrespectful would be if you were specced to have your pet tank and it was constantly pulling aggro from your tank.
BM hunters can still do really good DPS, especially if they spec right. The amount of damage a pet can do in the BM spec is amazing!

You could respond to them by saying, "Actually, when you're overgeared BM is an ideal spec for running heroics. I do maybe 5-10% less damage, but I also do less than half the threat, because the threat is split between my pet and I."