My position is that anyone can have any opinion they want, and that the significance of that opinion to others depends on whatever level of trust the claimer can command. This puts some people in a de facto privileged position. This can be rational (e.g. privileging an oncologist's opinions on cancer over a layman's) and in other cases not (privileging a fellow mom's opinions about vaccines over an immunologist or toxicologist).
So my point is that you CAN make any of the claims you suggested, but your authority won't carry much weight because you're just a random bloke on the Internet. You would have to make a convincing argument. However even then there are lots of very credible-sounding arguments out there that don't sound credible to someone who has actual knowledge.
The bottom line is knowing the truth of any claim is quite difficult, particularly when it involves jargon. In general the judgment of someone who has spent some time studying an issue is more be trusted than what "stands to reason" in your own judgment. Even so, an expert should still be able to give a coherent defense of his positions.
So in the case of this frog meme, I have no particular reason to doubt ADL; however if it were important to me I would look at the evidence ADL puts forward in justification of their position. I do not necessarily agree with ADL on everything (e.g. on Muslims displaying tokens bearing the Shahada), but they have more than any other group tracked violent extremist groups and their affiliates and therefore are in at least a position to compare and contrast the symbols used. If, however, it were an organization like Kahane Chai, I would feel no particular reason to look into their reasoning because they're a racist group. Life is simply to short to treat a source that is consistently nonsense as if it might be credible.