Firstly, I have to admit I have not seen the offending post, so I cannot comment as to whether it was 'inflammatory' or 'defamatory' in any way. It was certainly obviously 'contentious' by the response.
I still don't believe anyone was trying to be offensive with the comments evidently made, but again I cannot speak with full knowledge. I also do not for a moment suggest that posts should be literary masterpieces, worthy of Dickens, Shakespeare or even a play by Ernie Wise 'wot he wrote' etc. However, it can be very easy when using a keyboard to hit the wrong key, and sometimes type what can only be construed, as rubbish. I do it all the time as I am a one finger typist. So, do read what you have typed before hitting the 'submit' button, and if you do make errors, and we all do, then post a correction. However, if you do feel that your knowledge of the English language is not what you would wish it to be, then there are plenty of Courses available to assist. I admit that I have done far more studying since I left school, than the amount I achieved within those hallowed walls. The incentives of providing for a family, or endeavouring to get promotion, were pretty powerful. I also found that the ability to communicate in the written format was valued above many others.
There have been comments regarding the lack of a 'spellchecker' on the Forum. There is in fact an easy answer. Type your post as a word document first, and the computer will automatically check your spelling for you. If a green line appears then the computer is telling you that your grammar is incorrect, and probably a comma needs to be inserted somewhere. One word of caution though. Do check what language your computer is using. Many computers are US sourced and as such default to US English, which as we all know is very different from UK English. If you do not wish to be reminded to change an 's' for a 'z', or remove a 'u' from 'colour', then use the UK version of English. However, even that version is not perfect and I freely admit to having a well thumbed Oxford dictionary above my computer. A few seconds to check is all it takes.
I can comment that in the last few months, one post certainly did catch my eye for the reasons being discussed. It consisted of 8 lines of writing, all in one single sentence. Not a comma, colon or semi-colon anywhere. After reading it several times I eventually discovered that the single sentence contained about 4 separate points, but as written they were meaningless. It was irritating I do admit, but then the moment passed.
I personally am not denigrating anyone's literary abilities, but think about the following. If you are working in an industrial area and you see someone doing their job incorrectly, do you ignore them, or politely show them where they are going wrong? You are not accusing them of being ignorant, merely showing them the correct way, and as such everyone can benefit. After all their training may have been insufficient to equip them for the job entailed. However, as mentioned the key words are 'politeness' and 'assistance', not criticism, and although it is indeed Christmas, these are things we should follow the whole year through.