It sounds like the sharrows are there to give bicyclist the same rights on the road as cars. Maybe they're there more to inform the cars that a bicycle could be in the lane than for us. If there is a slower moving car on the road, you don't expect him to move to the shoulder to allow the other cars to pass. It's the other cars responsibility to pass safely. Same for us. Even without the sharrows I would take the lane to keep me safe. Which is our right as vehicle operaters. Don't you take the lane at times to make your ride safer for you? If so, sharrows are there to impower your right to do that.