I believe that Dr. Faustus makes his own choice: he has free will. While he may believe he commands the powers of darkness, only after he trades his soul has he actually become enslaved himself. Everything that happens to him is his fault. Perhaps his sense of superiority and ego cloud his better judgment.
In Scene III, Faustus makes it known to Mephistopheles that he knows exactly what he is doing; he has conjured, has rejected God and has thrown his lot in with Lucifer. Mephistopheles tells Faustus what a man must do to draw the attention of the powers of evil. For in these actions, the servants of the Devil see the chance to turn a soul to darkness and claim it.
… when we hear one rack the name of God, (50)
Abjure the Scriptures and his Saviour Christ,
We fly in hope to get his glorious soul;
Nor will we come, unless he use such means
Whereby he is in danger to be damned:
Therefore the shortest cut for conjuring (55)
Is stoutly to abjure the Trinity,
And pray devoutly to the Prince of Hell.
Faustus says he has done all that is necessary. He promises himself to Belzebub (Lucifer), and is unconcerned with the consequences ("damnation").
So Faustus hath
Already done; and holds this principle,
There is no chief but only Belzebub; (60)
To whom Faustus doth dedicate himself.
This word “damnation” terrifies not him...
Nearing the end, in Scene XVI, Faustus is stoic and reasonable about his fate:
But Faustus' offences can never be pardoned: the (15)
serpent that tempted Eve may be saved, but not Faustus.
The Scholars encourage him to ask for forgiveness, but he cannot.
Yet, Faustus, call on God.
On God, whom Faustus hath abjured! on God,
whom Faustus hath blasphemed! Ah, my God, I would (30)
weep, but the Devil draws in my tears.
Faustus entered into his agreement willingly.
Faustus recognizes that he knew what he was doing when he made his deal with Lucifer. Perhaps his ego blinded him to the true extent of what "damnation for all eternity" meant—perhaps he could not conceptualize it, therefore felt no fear of it. Either way, he does not make excuses for himself, but assumes responsibility for his actions.