So even if you keep your own coins secure, there is still a danger of theft performed with violence. You have heard of people who were forced to give up their coins/keys under duress.
Does this mean that multisig is a must?
No. Absolutely not. It is not needed. If someone uses method of stealing or extortion using violence and/or blackmail then I can used to steal anything from you.
It does not matter if you have great safe with gold bars at your basement, if someone will point a gun at you I bet you will gladly give them your money no matter what.