First, single sig, of any kind, is a dead end, not only for the hodler, but for everyone. If villains can reliably obtain funds by kidnapping and torture, they are incentivized to do so. In a fiat system, a credible deterrent is that transactions are reversible. In a btc system with final settlement, the only plausible deterrent is if kidnapping / torture will reliably not work bc a person, even subject to the highest levels of duress, cannot provide access to their btc under these scenarios.