My evaluation is that the
original usage of the "sealioning" accusation was
indeed as a generic dismissive, and its application was dishonest as well; I don't accept the term as a well-founded descriptor of troll behavior in the first place.
If you look at the original comic[1], the sea lion follows the couple around in public, into their house, and even into their bedroom, without permission; that is what makes the sea lion's behavior bad (criminal, in fact). However, "sealioning" in practice refers to people responding to public internet comments with other public internet comments. To treat the latter like the former is dishonest.
Furthermore, the sea lion is objecting to unsubstantiated criticism of his species, which is a form of bigotry. Imagine people searching Twitter for criticism of, say, their race or religion and arguing back at it. I suspect that 90+% of those who complain about "sealioning" would consider that behavior permissible and probably downright virtuous (and would add that the arguing-back need not be scrupulously polite). I'm frankly surprised that "social justice"-associated people managed to decide that objecting to speciesism was worthy of mockery. I think they just really wanted some term of disparagement for their opponents, and happily accepted this one when it appeared without analyzing it too closely.
[1] http://wondermark.com/c/2014-09-19-1062sea.png