There is a certain nobility in an honest opponent who tells you in polite but no uncertain terms that he or she will actively oppose your position.
Such individuals may be frustrating or stubborn but they are far better than these characters:
The Questionable Ally. This person joins your project not to support but to transform it. Indeed, you may suspect that this ally is not really an ally at all but a saboteur. One objection after another will be surfaced, ostensibly in the name of helping, and yet there appears to be no real reason for the continued delays, misdirections, and whining other than covert opposition. Never operate with the assumption that the more allies you have, the better. Some allies are giant burdens and you will move more quickly and more effectively if they are on the sidelines.
The Interrogator. This individual does not pretend to be an ally but does pose as an impartial observer. The objectivity is suspect, however, as the questioner seems to take a certain joy in pointing out your project's faults and none of its virtues. This person's creativity is devoted solely to noting how your goal cannot be achieved and never to how it can.
The Alibi Artist. This team member produces excuses instead of objections. Blame is ascribed to others or to the lack of resources or to poor timing and news of poor performance is delivered with a shrug. One characteristic of this type is a distinct lack of commitment to the success of the project. That may be denied, of course, but words of commitment mean far less than actions. Give this person an unimportant assignment far, far, away.
Deal with these types long enough and you may wind up according your honest opponents a strange and new respect.