Well one of the cons for sentient weapon would be they would never be seen as a full person by the majority. After all they were created as a tool meant to be used, not to mention that they usually don't have their own physical agency. In my mind that might develop as resentment of a kind over time. There are many stories about cursed sentient items that are hazardous to their wielders. This in turn might give sentient weapons a bad reputation overall as people might fear kind of rebellion at least, or a complete mental takeover at worst. A person with a sentient weapon can be seen to be "influenced" and never fully trusted depending on the world's history, and relationship with these kinds of things.
It may be a useful power to be sure, but nobody likes to entertain the possibility of your tools turning against you. That's why they're many horror movies with this exact premise. For the majority, this might take the form of further mistreatment of such tools in order to exert a feeling of control out of a primal fear, which would perpetuate a cycle of abuse. Honestly for a perfect sentient item with its own will, I don't see it being treated well except by an extreme minority, not realistically anyway. Humans are terrible creatures who mostly like to exert our will over others.