Silverlight never had even the slightest hint of security, and no interop with JS or non-CLR (e.g. JVM) languages.
It was also comically slow and worked only in IE.
I'm well versed in security of Wasm. Much better than anything else available today or in the past, obviously still not perfect.
One of the best features of Wasm is entirely social - seems like everyone has agreed on it, finally. That's enough for me even if it was a 1:1 copy of JVM or CLR.
So says the marketing, usually pushed by those with an agenda with WebAssembly, forgetting about all those that trace back to the early 1960's and mainframe language environments with capabilities.
Lets sell old stuff as something new, never done before, rewriting history.
More recent chapter, application servers with WebAssembly, what a great idea!