I pay ChatGPT money and I have more confidence they've thought about XSS and what might happen with malicious payloads. I guess ChatGPT is less deterministic. Maybe you're right and I'm not paranoid enough, but I would prefer to use an offline tool (and using an LLM does seem worthwhile since it can do more, I can guess it's base64, the LLM can probably tell me if it's something more exotic, or if there's something within the base64 that's interesting. I can do that by hand but the LLM is probably going to tell me more about it faster than I can do it by hand. So it's worth the risk, while pasting it into base64decode.org doesn't seem worth the risk vs. something offline.)
If you think that there's obvious answers to what is and isn't safe here I think you're not paranoid enough. Everything carries risk and some of it depends on what I know; some tools might be more or less useful depending on what I know how to do with them, so your set of tools that are worth the risk are going to be different from mine.
That makes no sense.