Are the criticisms against Dart valid?

Question

According to this Wikipedia article, Microsoft, Apple, Mozilla, and others criticize Dart, a programming language Google introduced to work in web browsers, because they feel "it seems harmful (cf. VBScript in IE)".

But Dart also compiles to Javascript, so a web application written in Dart can run on any modern browser. So are their concerns valid? Can Dart really be a threat to the web's openness?