Asked another way, are you hypersensitive to the possibility of germs, or is the joy of already smooth butter worth any potential risk?
If it makes you feel better (and it should!), the FDA says that butter is perfectly safe at room temperature. That might not be an option for those of you with especially determined pets or anyone who doesn’t use butter often enough to justify leaving it out, but it’s nice to know there’s no actual reason to worry about it. Some habits are hard to break even in the face of such facts, however, and those of you who grew up with your butter in the fridge are more likely to keep it that way; if you’re such a person, just wait till you hear how many Europeans don’t refrigerate eggs.