According to the USDA, butter is safe at room temperature. But if it's left out for several days at room temperature, it can turn rancid causing off flavors. The USDA does not recommend leaving it out more than one to two days. Salted butter has less of a chance of spoiling on the counter compared to unsalted butter.
Yes. There are many similar products that are intentionally left out overnight in plastic bags in supermarkets such as cheese breads of various sorts.