It's not hostility. It's just that you're a very passionate Mozilla employee and a very passionate creator of asm.js. And from past experience I expect that you'll be willing to continue a debate longer than I can. Plus, you already know that I have reservations about asm.js, and it's just not worth rehashing that debate (accepting that WebAssembly appears to be heading in a direction that addresses most concerns, so I should offer well earned kudos on that front).
Getting back to your point, pragmatically speaking, maintaining a port is a distinction with less difference than implied. First, any reasonably complicated NPAPI plugin needs to handle a range of browser-specific quirks, meaning that significant porting is unavoidable even if it's bundled into one binary. Second, Unity supports ActiveX in IE, so they're clearly already comfortable maintaining a browser-specific port that doesn't offer any of the security or platform portability benefits of NaCl.
Outside of that, there's just the one-sided nature of the argument. As a creator of asm.js you are obviously a huge proponent. However, you must appreciate that not everyone perceives it the way you do, and not everyone agrees with the path you chose for adding support into Firefox. So, the technical burdens on another browser are just not the same, and in the specific case of Unity in Chrome have to be balanced against the fact there was already a tremendous past investment in a high-quality implementation.
So, no, I completely disagree with the framing that "Chrome has left Unity no good option". Independent of any work in Chrome on better supporting asm.js, the fact is that Unity had at least one other good option. So, I'm sure Unity had their reasons for the path they chose, but it was and continues to be a very explicit choice.
