Agreed and if you looked closely at the Minuteman webpage (oooops don't ban me! I know we can't link to it but it's ok to acknowledge it exists right?) You will see that they are doing background checks on those that have applied to participate. They have also stated that any trouble makers that show up will be told to leave. They have made their declaration.
There is no evidence that the Minuteman Project welcomes or supports stormfront. Stormfront wants to go to the party just like they want to be on Free Republic and both groups have told them to stay out.
Since a lot of people know this that leaves the speculation as to why they were banned from Free Republic. One possible factor, for Minuteman being banned from this site, is that the organizers of Minuteman have clearly stated that this protest is an embarrassment to the Bush administration and they mean it to be.