It’s also intended to allow them to modify it for their own purposes, and provide the modifications to others who have a license to the original product.
Especially on the web this was finally possible, and now you’re suggesting to take this away again?
At most they legally protect someone who decides to run a disassembler or decompiler on a binary from prosecution or lawsuits (but only in as much as you don't use the result to violate copyright or other restrictions).
See Article 6 on http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:...
And "copying the decompiled source of the part of MS Word that reads .doc files" counts as covered, so, it's quite a lot.
Especially with websites, where you might want to interact with, or write addons interacting with, WASM threatens those rights.
What's a "valid" source map anyways?
Furthermore, debugging with sourcemaps is suboptimal. WebAssembly wants to support much better debug information than this.