Not proofreading also comes across as self-centered and arrogant. If other people's time is worth as much as your own, and 3600 people will read a message, then

Not proofreading also comes across as self-centered and arrogant. If other people's time is worth as much as your own, and 3600 people will read a message, then it's worth spending an hour making sure that people can understand it on average one second more quickly. Of course, most people value their own time more highly than others'. But even if that's the case, it's surely worth spending 5 minutes to get it right.