Free-standing centers tend to have low infection rates, they typically offer pleasant surroundings in newer construction, and parking's rarely a problem. Yet the proliferation of ambulatory surgery centers has some questioning if the lower cost comes at a higher price than people realize. Foremost among the skeptics are traditional acute care hospitals, which say the ambulatory surgery centers draw healthier patients and patients who are more likely to be insured. That leaves hospitals bearing a greater share of charity care.