You don't seem to want a right to decompile/disassemble (which you could do in the same form for WASM than for most other languages) but a right to directly view the original source code. Such a right does not exist in general. The owners of the source code (the intellectual property) may give you the possibility to view it, but they could also decide that they don't give it to you. The only exceptions I know of are if the creator incorporates other software parts which mandate releasing the source code, e.g. GPL libraries.

I know of no country (or other jurisdiction) where a legal "right to decompile" exists.

Many countries allow reverse engineering, and you could infer a "right to decompile" from that in some cases, but as far as I know none of them place any requirement on the source to make it easy.

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).

The EU has a very, very limited right to decompile for the sake of interoperability.

See Article 6 on http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:...

And for personal modifications, and so on.

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.

Browsers don't create laws. WebAssembly can't legislate. This is really out of scope!