Yes, new posters should go ahead and post. They may find, for instance, that yesterday everyone else had discussed their subject to death and someone is not shy about saying so. Just say "Oh, I wasn't here then, I missed it!" and don't assume that their answer is personally attacking you.
And after replying with a helpful answer to a post about (say) an 11 year-old grandson who insists on wearing a pink onesie to school, where the uniform is strictly black shoes and expensive grey trousers they may find (WILL find! in this case, it is a familiar theme) that the poster is a well-known prankster who starts several threads a year with (fake) school uniform problems, and that the other answers on that thread vary from a dismissive "Oh God not again!" to frivolous suggestions like apprenticing him to Danny LaRue.
They are not being cruel to an agonising granny - they have been round it before and they know not to "feed the beast". This is why people sometimes advise that new posters "settle in".
When you walk into a real-life room full of people (strangers to you) chatting, you DON'T know what has just been said before you enter, and you DON'T know the back stories of the comments they are making. Saying little and listening a lot for a day or two gives you a chance to catch up.