Does anyone believe the government is incapable of abusing their power, rigging evidence, mistreating prisoners? If a US citizen is entitled to the protection of due process why should an alien not be entitled to the same? Military tribunals just make the probability of such things happening much higher.
As discussed in this thread the fairness of a process is not judged by the outcome but by the fairness of the process itself and military tribunals do not meet the minimum international standards.
1- Trials should be public so that the public can be informed as to their fairness. Only exceptionally, and for good reason, should some facts, identities, etc. be kept secret.
2- The accused should be allowed proper legal representation without undue restrictions.
3- The accused should be allowed to confront and question any and all witnesses and evidence presented against him and to present witnesses and evidence of his own.
4- The parties should have the option of appealing the ruling to a higher court.
5- Justice should be blind. This is crucial and it means justice should be administered without regard to who is the accused, whether he be powerful or not, rich or poor, black or white, citizen or alien.
The US has criticised, and rightly so, other countries (e.g. China) for not meeting these criteria. A trial in China is a sham because the judge, the prosecutor and the defense are all appointed by and answerable to the Communist party.
Other countries have expressed reservations about the tribunals and the result of their use will be, overall, counterproductive.