I think the first two parts of this article showed the dangers of blindly using hashtags. It is like putting out a welcome mat for bots to follow and interact with your content.
Also it can drive false signals, that cause misinformed marketing decisions. As in 14.95 billion false signals from notifications per month. And unless you stop using them it will just cause a cycle of disappointment and questions on why your Twitter strategy is not working.
I don't know if it's a rule like Rule 34, but chances are they're very similar: Spam/Porn...what exactly is the difference, really.
I mean other than the obvious.