Try getting Mexico to hold a debate between the leading Presidential candidates on a English language network with questions in English only, along with a nice anglo-American, English-only moderator. You'd be laughed out of town for such a proposal.
Whatever the rights and wrongs of the debate, this is just a silly comparison. Does Mexico have an English-speaking minority that is over 40 million strong? Do they have an English-speaking minority large enough to sway the course of their presidential election? Of course not.
Like it or not, the US is home to the 5th largest Spanish speaking community in the world and the majority of them live in states the Republicans have to win to keep the presidency in 2008. This is not the old Cuban community that can be placated by keeping the embargo on Castro in place.
One thing that Bush and Rove did well in 2004 was to gain support in the Hispanic community. Are you really willing to throw all those gains away for the sake of standing on some pointless principle?
Tancredo is staying away because he's nothing to lose. His candidacy is going nowhere and the only way he can stand out is to take a hard line on this issue. This debate is no more divisive than the values voters debate they had a while back. Do you think the 30 million or so American non-believers felt the warm embrace of the Republican party as their candidates talked God and pandered to the religious right?
If they are American citizens and can vote, they should know English. Why should the candidates depend on translators to communicate their message? We need to make English the OFFICIAL language of this country or we will be Balkanized along cultural and linguistic lines. We see what has happened in Canada.