How id that being douche? I do it all the time. My healer is able to dps so I flag as both. It makes finding a group much faster.
You are just gimping to group by dps-ing in heal-spec. It IS a douche thing to do. Field respec is basically free, get it and learn the dps-specs. :P Your damage amounts to absolutely nothing in heal-spec and your resource pool just goes down the drain.