I've been browsing these forums and google and so on but I haven't found much usefull info about shadowpriests in endgame PVE.

I'm a warlock myself and I'm trying to convince my guild that a shadowpriest (1 shadowpriest) in the raid is a good idea. Because of the increase in damage caused by warlocks due to shadow weaving and the constant stream of healing from VE wich means I can lifetap just about enough to keep spamming shadowbolts throughout even the longest of fights.

I'd group the shadowpriest with 4 warlocks who all are capable of matching even the best of mages on total damage done through a complete MC clear. All I want is 1 shadowpriest, but they keep telling me no. (1 of the priests is even VERY much keen on respeccing to shadow, but they say: "If you spec shadow don't count on us bringing you to MC or BWL".)

I need your opinion as I really don't think my guildies have given me a single valid reason to not have a shadowpriest in our raids. They keep asking me who to replace and I pretty much say anyone but warlocks as we're the ones benefitting the most, but they won't listen.
Now Please give me some sort of reason that will make them understand that the 1 shadowpriest will make the raid stronger or tell me that I'm a n00b and that they're right. Either will give me peace as long as I get some good valid reasons.