This includes bombers. If you want to dogfight pick, a different plane. You can dogfight with P-47's if nobody else is around. Your primary mission is to survive. Your secondary mission is to kill bombers.
Targets of opportunity are just that.
If someone gives you an opportunity by all means take it. If they don't give you an opportunity, do not force the issue. Get used to your opponents calling you names when you do so. If you leave because you are unable to secure advantages, work to get those advantages and return. Alternatively, hunt somewhere else.