If someone is trying to achieve a goal through (what they might not know are) impossible means, "letting them be" isn't going to help them.
Although it might not seem very helpful (and indeed there are better ways of helping) pointing out the flaws in the approach is contributing more than "letting them be". Doesn't cost a thing to be civil about it though.
ITT: people giving wrong answers to a post linked to a blog that answers the question 'What is PID 0?'