Maybe it's "normal" for you, but I think other people would consider it rude, arrogant and unnecessary.
You must have been very busy in Thailand correcting their English every step along the way in your conversations with them. However, have you noticed that they never correct our tones when we try to speak Thai - (unless we ask)? It would be considered rude in the extreme.
Over the years we have had many members whose first language is not English and who made numerous spelling and grammar mistakes - Christian excepted. Yet you never corrected them. Didn't you think you should have, given that it's a "normal part of discourse"? Obviously not. You choose who to correct and who not to. A little disingenuous, don't you think?
There should be a semicolon after "indeed", not a comma.should never be challenged, indeed if anyone
I trust you appreciate my correction!