A messy claim about the great replacement theory.

The statement is so rambling and non-specific through slippery words and innuendo, that I don't think it is worth writing a book to illustrate all the errors. I suggest you ask the "someone" who wrote it to write something more focused. Keep in mind, language is first a tool of thought and secondarily a tool of communication. The attempt at communication in the statement suggests a disordered thought process.

As the NRA protects the Second Amendment...

I wouldn't say this was a non sequitur ; just that it is irrelevant. You can substitute anything here similar e.g., "As seat belts protect your lives..." It might also be begging the question . It is debatable if the NRA really protect the second amendment. Now for the rest...

you should protect your white rights ( just as BLM for blacks) if not you will lose them  one day.

I am curious what "rights" I have as a white person. I think they are conflating this with human rights. A reasonable argument could be made that we should protect our rights (as Americans, or whatever country) or they will be lost. I don't see how race fits in here.

When the blacks and browns population over rules the percentage of white population you will become the minority and then you will be  looked down on and that will not be a good day.

We can reasonably say that whites will become the minority (in the US at least) in the near future. But this is a different "argument" now. We shifted from "rights" to perception. There is no right that says white people must be looked up to.

Yes, this claim is a mess.

"As the NRA protects the Second Amendment you should protect your white rights ( just as BLM for blacks) if not you will lose them one day. 

The reason this is so rambling and discursive is that it is not a coherent train of thought, but rather a hotchpotch of erroneous, ambiguous, and selective arrangements and misinterpretations based on propaganda and belief. Arguing against it is a fool's errand and the equivalent of playing chess with a pigeon. 

While the NRA "claims" it is protecting Second Amendment rights, in reality, the NRA is only protecting their own selective interpretation of a deeply flawed amendment in the Consitution that has vexed scholars, courts, and legal experts for centuries.

If one is foolish enough to take the bait one would have to challenge the claimant's references, citations, and sources, and one would have to respond accordingly. Blanket declarations without evidence are not logical arguments and can be readily dismissed as such. In fact, they are so baseless they do not even qualify as errors in reasoning. They are just fanatical rantings.