As a wizard, Beam Kiting is anti-social and interferes with other people's use of a zone. Since you can't be sure when people would like to use a zone, I don't think there's ever an excuse for disrupting it (even doing this in instances causes the instance server to do more processing than it should, and potentially disrupt play).
Beam Kiting in Icefall has caused my group mates severe disruption, it stops mob respawning and causes massive zone lag. While I think the root cause is a problem with the pathing in Icefall, the impact is only caused when someone beam kites 50+ mobs.
Hopefully they'll put a target count limit on the beam spell asap to prevent this kind of abuse.
Edit: It has the same negative game impact as ShakerPaging, and I was glad (as someone who also plays a warrior) when that was fixed for the same reasons.