Are passenger/cargo ships viable targets?

[Missing Name]

I attack them, because they are Passenger/Cargo ships. You never know if they are carrying a load of 40mm AA shells or rations. Also, any armed merchant is showing intent to shoot back. Which is why America often loses some ships during poor visibility in mid-1941.

I have a love/hate relationship with P/C's. They so much determination that I must admire them. But at the same time, they're hard to sink for whatever reason.