When I opened my first indoor, I also felt that our sound was too loud. Someone over at another forum suggested that, in most cases, this was caused by equalization issues. After having my rooms professionally EQ'd, then buying the equipment to check it now and then, I found that the industry spec was reasonably comfortable.
That said, I don't feel that leaving the volume at "7" should be a religion. Yes... trailers are usually way too loud. Even the experts find ways to drop the volume at that time. If trailers can be too loud, so can a movie.
My feeling... If God intended us to leave the volume at "7", he wouldn't have given us a volume control.
In the end, everything about your business reflects on you, not Dolby. If you feel you need to make an adjustment for the comfort of your audience, then make it. However, if you're always set at 4 or 5, then something's not right in the booth.