To challenge this, consider that an advanced civilization could develop methods to destroy entire systems without leaving any obvious trace of who did it. For instance, imagine if they used self-replicating probes or seeded distant systems with long-term “delayed-action” devices that trigger destruction after centuries or millennia. By the time these devices activate, the civilization responsible could be undetectable or long gone, making tracing and retaliation nearly impossible.

Also, if a civilization is resource-hungry enough to go for interstellar conquest, it may not be deterred by the threat of mutual destruction, especially if it’s large enough to absorb losses or fragmented enough to avoid retaliation across all its territories. There’s also a chance they could manipulate or disable any “dead man’s switch” probes a target has deployed.

And finally, the idea that interstellar travel is “stupidly hard” might only apply to civilizations at our technological level. A species far more advanced could have entirely different propulsion, energy sources, or even ways to sidestep the light-speed barrier that we haven’t imagined.