People can learn or assume whatever they like, people will assume things anyway whether your careful or not. The point is that I control my online presence so that nobody can justifiably come to conclusions about me that I would be particularly worried about. I treat my social media interactions the same as I would my personal interactions. I do not make jokes I would not make in public, I do not make comments I would not face to face. In fact I would suggest I am less likely to do something stupid in that media than in person because of the detachment and chance to read what you are posting before clicking to submit it.
#10 is his only real justification, it's true that it isn't for everyone just the same as going out on a Friday to the pub isn't for everyone. The other 9 are simply the same tired arguments that everyone makes to try and justify their attitude in #10.
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