Yes it goes more underground IMO. It's like the anti-immigration movements in Europe and the racism towards immigration prevalent in my own country, Australia. It's there, it gets press coverage, how big it is is debatable (here at least) but official policies go on regardless. Yes you are free to join any group or party that is against immigration/alien alliances but will you win any elections and actually change policy? I don't think the Terra Prime supporters, for all their noise and visibility were able to produce the numbers to get the votes. Likely they were seen as extremists even by people who feared alien contact and sympathized with their policies.