This is the nub of it, isn't it? It's Marta's belief in the truth of the first statement--and she's got a point--that activates the sentiments of the second statement.
That doesn't make it right--that second statement, it's wrong, it's xenophobic, it's counter-productive--but when the left appears to bypass one group which deserves our support in order to support another, it's understandable when members of that group see that (possibly correctly, too) as discrimination against them.