> I don't think I did such a thing.

Yes, you were more subtle about it, calling him inexperienced rather than stupid. I see little difference between the two forms of ad hominem and that is what I wanted to point out.

> which is even less convenient than Forth's syntax

The two versions are syntactically the same. You can take a piece of Forth code and do the substitution:

  s/if/[/ 
  s/else/] [/
  s/then/] if/

You then have some Stem code that is slightly shorter. The Stem syntax is just a generalised version of the Forth syntax. The only exception I can think of is it being harder to compile, but as you said, that tiny bit of speed doesn't really matter on modern systems and additionally the code would likely be optimised to the same instructions in a JIT.

> You want the system to keep quiet when you give an hint that you do something on purpose

Why? No code that's saved in production should ever redefine variables, so it's a warning you'd get exclusively during interactive use at the REPL, where you'd be free to ignore it. It's easier to ignore a message than it is to tell the system not to give you that message.