It's no mystery that there's opposition to a bill which is a messy compromise between opposite agendas. Conservatives hate it, and prominent Democratic politicians haven't really expended any effort to make the liberal case for it. It's sold as a fix to a problem, without either the "fix" or the "problem" being clearly defined. It's Broder Politics at its worst.
The more liberal view of immigration is much more popular than I ever imagined, and it's a shame that Democrats haven't used the opportunity to rally any support for that view. It's what happens when legislation begins as behind-the-scenes compromise.