They might not be doing this now because there is ~0 consequence to advertising ICOs via PM today, but if advertising an ICO via PM meant the ICO thread gets locked, I would think some would engage in moderate advertising via PM for their competitors.
And how would you know the person sending the SPAM had the PO's permission? Are you suggesting that and your massive scam army can shut down any ICO just by sending people PMs promoting it?
The OP is suggesting that if anyone advertises an ICO via PM spam then the relevant ICO thread gets locked. I am saying if this were to get implemented, a competitor could advise a competitor of theirs via PM to get their competitors thread locked.