First off I'd like to preface this by saying I have lv50 all jobs/classes so there is no bias against crafters or w/e here. I don't know about anyone else, but I'm tired of carrying people who want to cash in on crafter materias through WP/AK/CT/CM etc. Wearing class appropriate gear to SB in any dungeon is perfectly fine by me, but wearing a full set of lv 30 crafter gear to make T2 crafter materias is unacceptable and should not be tolerated. Is any one of those instances hard? No. Can you do it with 1 in the group geared this way and it not really affect the outcome of the run? Usually, yes. But for example, I've had numerous CT runs where a DPS was in full crafter gear at the Atomos fight cause slow dps on adds, which caused 3 adds to spawn, which wiped the group, and then wiped the entire alliance, most of the time with the offending party having a very 'screw everyone' else attitude. CT is already bad enough with the steady influx of trolls berating players that are new to the dungeon, all this is doing is exacerbating an already annoying problem. Some people will undoubtedly respond to this with 'that's what the vote kick feature is for,' and that would be great, except plenty of the aforementioned offenders join in groups, and I personally have been vote kicked for harassment by calling a member out for this exact behavior. (By calling them out I mean saying nothing more than wearing full crafter gear in a raid is BS, which it is.) Again, I don't know about anyone else, but I don't run dungeons to make gil for random trolls.
Edited to get around character count in wall o text.