The problem is that liberals and moderates can try to compromise on issues that freepers SAY they care about (border security, employer penalties, tax collection), but bottom line, what they really want are fewer Mexicans (and "Mexicans") coming into the country.
So you can either try to bend over for a faction that absolutely won't compromise, or you can forget about them, try to put together a policy that would actually rally support from a center-left coalition, and hope you get enough votes that way.
I'm not sure the latter would work, but the former already failed.