The term "Latinx" is offensive for several reasons:
1) Indios: people of pure Siberian-American blood, whose descendants did not mate with Europeans, should not be called anything "latin"-related, as it implies they are part European. It's kind of like Mormons baptizing dead homosexuals.
2) Mestizos: people of part Siberian-derived blood whose descendants did mate with Europeans did not necessarily mate with Europeans from countries with a thorough grounding in "Latin." While Latin did spread through conquest, and did influence many of the languages in occupied areas, many of the subject peoples never spoke Latin.
3) Northern North America: Siberian-derived peoples who were at one point conquered by the English are not part of "Latin" America in the sense of being part of a Spanish empire, and should not be slurred with an epithet mistakenly meant to target those from South or Central America.
4) Sexual Identity: people with presumed roots in South or Central America who transition should not be insulted by the use of a mathematical variable, e.g. "x," standing in for the identity they have worked so hard to cultivate. Using an "X" would imply that a so-called "Latino" or "Latina" was indistinguishable from others of all sexes and gender identities belonging to that person's group, and that their choice or effort to transition to identification with any established sex is voided merely because another person wants to avoid adding a few words.
5) Implied European Supremacy: using a blanket term derived from a European language to identify the descendants of the European colonial sphere, rather than forcing the development of a pre-Spanish-arrival South American/Siberian-American language term, implies that the people who might be called "Latinx" have no interest in reclaiming the lexicons of their ancestors, and/or that those languages are not sizable or descriptive enough to be used in conversing about or recording events that happened from 1492 forward.