What happens, I think, is that English is our world's lingua franca. I am not a Native English speaker, yet I'm using it every day, in my work (for which I'm paid), and in my passion (which is writing). I'm constantly striving to be better, especially since I have only learned English on my own, and not in a formal environment.
I understand that for someone who is a Native English speaker, the mistakes done by non-Natives must be bothersome and even funny. I wish my writing was completely free of mistakes. Having an editor really helps.
However, I must point out something. When people who use English as a second language talk among themselves, mistakes do not count as much. I have written plenty of fanfiction and got comments from people from all corners of the universe, and it showed in the way they were writing their reviews.
But isn't it a bit wonderful that someone like me, from Eastern Europe, can write something, and be read by someone who's from the Philippines? Without the English language as the communication vehicle, that could not have happened.
Don't get me wrong. If someone is looking to get published and wants to be taken seriously, they should proofread their work. Yet, it's a learning process for a lot of people, and, as long as they do not write absolute trash with total disregard for the English language, I'd say they should continue. And they should also accept constructive criticism because that's the way you can grow and learn.