Some people believe that these two are one and the same and are conflating the terms in order to discredit those who want to protest against Square Enix's current decisions.
A lot of those who think this is the case, then don't seem to know how economics work.
Boycotting is one of the only tools at the disposal of the CONSUMER to protest against a company's decisions.
The protest is made by also pointing out the reason WHY someone would be boycotting X product.
We are under no obligation to be SE's customers, as such we are not obligated to buy Shadowbringers or to sub. It is our own choice to make, whether we support SE or not.
Since boycotting is a form of protest, and protest means that it is meant to have an effect on the party that is targeted. It is at its very core meant to "hurt" the party in question, because of a variety of reasons on the customers' part by not buying the product.
In terms of legality, what people are doing is in no way "blackmail" and those who entertain such a notion, entertain a fantasy.
I'm sure some may be bluffing when it comes to unsubbing, but for me it's by no means the case. (Although it's mainly for BLU)