on one part not having a full party of herloom people slows down the dungeon to a fucking crawl and makes it pretty fucking infuriating to run as dungons are the quickest way to level up by far so kicking non heirloom people is in your best intrest by like a lot of time (i have had some dungons take 4 times as long since i was the only one in heirloom gear)
on the other part you are super douch defender of douchland if you start kicking those people.
the question is how do you fix this? i can think of a few ways.
flat stats for all dungons and specs (as in dungon X means you have Y stats for specc Z). this way it no longer matters if you have heirloom gear or not when it comes to damage and healing everybody has the same capabilites and if blizzard is working on that downlevel to play with your friends thing this would hit 2 birds with one stone
the longer the instance gose on for the more powerfull you get as a way to force people threw the dungon even if they are in shit gear. you wouldn't start getting the buff untill what an avg clear time is and it would quickly make you more powerfull so in the end it dose not take the much longer to clear a dungon with a noob as with a full party.
split heirloom users from non heirloom users. this would put first timers with first timers and they can have fun trying the easy dungons for themself and in the case a heirloom guy and a non heirloom guy would que up it would be in the non heirloom que. the issues with this way is the que times would likly just be horrible but at the same time having first timers play with first timers is somthing you should want as they really get to experiance the dungon then no vet trying to push threw inorder to get exp.
award extra experiance based on time (longer time more exp) or helping a team of baddies get threw a dungon. (you are the main guy helping the group threw in one way or an other) the big issue with this idea is that it is rife with beaing to be abused.
this is just a few ways i can think of inorder to discourage kicking bad people. i personally think idea 2 is the best as it also means how long a dungon takes becomes very predictbal and the hassle and time of kicking a person would not be worth it in terms of time.