Any conversation

The fear of being bad at it is the only thing holding you back. I experienced something like that with playing music with others. Perhaps you could learn to lay down your critical brain during the creation process and that good/bad isn't a useful distinction until later when you're editing your work.

I like to write whatever's on my mind, or questions on the rare occasion!

I don't think so. I have been using more open source software than ever before. You may argue that with LLMs I have the power to make my own stack of things, but this doesn't eliminate that I still need knowledge to properly steer an LLM to create something worthwhile. If I have no knowledge of what I intend to build, the best thing the LLM will generate is a half-assed copy of something that already exists. Which is what we have been drowning in the past couple of years.

Of course not. I think it is much more relevant to ask "Is closed source dead?". Anyone can now replace a proprietary program with a vibeslopped alternative which might suit them just as well. It will have the same level of trust (ie. none) and none of the other drawbacks.