Sentence:  The problem is that, much as we may sympathise with those coming in and expecting different rules of discourse than obtain here, we are not obligated to change our ways to suit them, and people who don't perceive that fact fairly quickly (or fail to "get" it after the first time it's pointed out) and continue to <WSD>grotch</WSD> about how "You kids are playing wrong -- play right!" are Fair Game for sardonic replies. 
Meaning of the word marked with <WSD> tags:  To complain.