From a rational and removed standpoint, it is clearly not acceptable. There are some confounding factors here, however. For one, Google specifically advises to use their hosted version of the font instead of self-hosting. Another issue is that these people are clearly frustrated by the nonchalant attitude of the maintainers when it comes to breaking others work.
If you are telling people to use your hosted version of your open-source contribution yet have no care for responsible stewardship, you are being irresponsible at the expense of others.
If you don’t want emotional responses after purposefully breaking the hard work of many, you are being unreasonable. While we should strive to be respectful and courteous under such tension, I can understand that not everyone is successful every time.
In other words, I think empathy should go both ways here. Usually, I find that others act very unreasonably and rudely towards maintainers of open source contributions. In this case, I think both parties have made mistakes that deserve forgiving (but not ignoring), including the rude emotional reactions. Both parties should apologize to one another.
Imagine all the sites you ever worked on suddenly broke and all your clients called you demanding satisfaction. This is a direct result of something Google has done after telling you they wouldn't (you could infer this according to their guidelines saying not host the fonts yourself).
Being the nice guy you are, you bring the issue up to them and give them a very reasonable solution.
Not only do they ignore you, but they do it again.
The maintainer is being remarkably thick-headed. The font has been accessed 3.65 BILLION times. A designer from Nike is posting on the issue. A LOT of people use this font, this is global. When someone comes to you with an issue (a big one at that), you need to do more than just say "eh, too bad, do it yourself".
Wtf is the point of google fonts if I can't rely on them to serve fonts? What is a "Font" anymore? The new "version" isn't Montserrat, it's Montserrat2, and it's been hotswapped with Montserrat.
