I am also against adding captchas for writing every post, and it would create big decrease in forum activity.
Maybe adding captchas could be considered for people who are writing many worthless posts in short amount of time.

@LoyceV can you check and test this tools I found for detecting AI bots?
This tools can be used freely and it's called GPT-2 Output Detector, GLTR and GPTZero.
They are not 100% correct all the time, but they can be indicator if someone is using AI for making posts.

Sources:
https://openai-openai-detector.hf.space/
http://gltr.io/dist/index.html
https://etedward-gptzero-main-zqgfwb.streamlit.app/