a) Health: Most of the studies are VERY preliminary. Only a minor correlation has been found between gas and childhood asthma. And the studies mostly confined themselves to home environments. Commercial kitchens already have much higher standards for ventilation quality.

b) Environmental: I think a good case could be made that eventually gas will go away as we transition. But currently it's still being burned off at the wellhead in the US as a waste product. It also only puts out a tiny carbon footprint compared to coal or oil - which would make it a slight improvement over using the average city power grid right now.