*sigh* If you like healing and dpsing in a dungeon that's good for you. Don't go around saying what you do HAS to by done be everyone. I' don't dps in dungeons very often because the dps has already killed everything before I could even get one spell off. I heal and dps because it's my personal preference and I do get bored when not doing anything.
Hells, I've ran dungeons with healer who dps and those that don't. It's no sweat off my brow what the do as long as we get the dungeon done. Is it that really hard to understand? Many people play the way the want as long as they are doing their job or not causing the party to wipe it's all good. So, throwing out "They are lazy" is really....um, ridiculous.
Some people who play healer just want to relax so they don't dps. Others are not very confidant with their ability to do both. So forcing your personal view on someone while saying SE made it that way is lame. No, leveling a healing job and doing story quest would be hard if you didn't have any offensive skill. So, play the way you see if and they'll play the way they see fit. If it's not causing any real harm then it's not a problem.