Gaming has a lower impact than going out for entertainment. If people stop gaming, they're not quietly going to sit in the dark instead...
You could also say sports ruin the environment. A more active life style needs more fuel and the food production chain is the worst offender for CO2 footprint. When I go cycling for hours in the summer, I come home, cold drink, burgers on the bbq, get those energy and protein levels back up. I eat and drink a lot less during winter.