Sure, the primary burden of proof is on those proposing a change. However, any time you stand up and make an argument, the burden is on you to make sure it actually makes sense, and that goes for both sides.
This is getting a bit meta, but I disagree. It would be trivial to abuse in discussions.
A: Bash would be way better for SQLite, really!
B: But Bash is a terrible choice because X, Y, Z, ...
A: If you make those arguments, you have to prove them.
I'm not sure I take your point. If X, Y, and Z are cogent enough to be worth a rational response, B has done their job under my principle above. A is precisely the one I would want to yell at for using specious arguments.
Anything that is stated without proof can be refuted without proof. Why you think your opinion should be regarded at a higher standard than anybody else's?
...I don't. That's sort of my point. Both sides of a debate have the same responsibility to be reasonable, whatever that level of responsibility may be, whether it's a formal debate or just tossing ideas around.