If AI is a weapon (possible), open source is how the populous maintains freedom against corporations or governments. It’s unclear how the public keeps up with the arms war when privately trained models can have access to a wide collection of data that’s not publicly available.
AI is not a weapon. AI certainly, like every other information technology ever certainly has applications to weapons and warfare. It also has an enormous array of non-weapons applications.
If you read the GPT-4 technical report you can see that the unrestricted model (that people could be running at home) are capable of some pretty large-scale horribleness.