Yeah, denying because it means more profits isn't okay. The fact that these insurance companies are publicly traded and have to maximize value for shareholders creates even more of the wrong incentives.
These should be not-for-profit entities, with appropriate controls.
Many private health insurance companies are not-for-profit, including such large organizations as many of the Blue Cross Blue Shield Association licensees, HighMark, EmblemHealth, etc. Their coverage and claim processing policies are pretty similar to the for-profit companies.
And private health insurers generally don't make more profit by denying claims. Due to the ACA minimum medical loss ratio rule it's rather the opposite. When claims are denied it's usually due to decisions made by self-funded employers that sponsor health plans for their employees. The insurers are mostly just acting as administrators for those plans rather than providing any real insurance.
These should be not-for-profit entities, with appropriate controls.