Merged mining requires extra long polls when the NMC block changes. Everytime you have a LP, you increase the odds of users getting stales during that window where the pool is generating thousands of getworks for miners. MM more than doubles the number of long polls. The only way around that FACT, is if some of the other MM pools are not pushing out a longpoll when the NMC block changes. If that's the case, they're damaging NMC production without hurting BTC much (there is always some minor overhead in generating the work for a merged block vs a regular block).
You're right that longpolling on NMC blocks isn't worth of doing, I'm not triggering LP on NMC block, too. However I must disagree that merged mining is adding any measurable additional load on servers when doing properly (so - without merged mining proxy) or hurt bitcoin mining in any way. Also that drop in NMC performance because of not doing LP is really mininmal, in few percents, so that's nothing what really hurt anybody.
Otherwise I agree, introducing merged mining WAS pain and I really understand that you don't want to play with it when NMC price is so low (actually it's on 30% of price in time of MM started).