Before the policy change, aliens without proper identification would get in trouble for not having valid ID, since aliens must always carry their passports (or green cards) in the US.
Citizens were upset that aliens with consular ID's no longer had to prove that they were here legally if arrested, and may have been concerned that consular ID's are easier to forge and harder to verify than state drivers licenses.
Essentially, aliens would get a pass from the law if they carry a consular ID.
The protesters were assaulted and battered by some "counterprotesters" (immigrants/aliens) while Anaheim police watched and did nothing to intervene. If the crime were reversed, with American citizens punching and kicking immigrants/aliens, you can be sure the ACLU, NAACP, etc. would denounce the attacks as a "hate-crime."