Commentators are split over whether to interpret the italicized phrase as earthly rulers (Herod and Pilate, for example) or as demonic forces. But let us assume here, at least for the sake of argument, that it means demonic forces. I want to list a few passages that may shed light on whether or not these demonic forces may be standing behind human crucifiers of Christ, since it has been opined in some quarters that to interpret the text in this way is to (unfairly) read the human crucifiers into the text.
Here are the passages, in narrowing layers of relevance.
There are spiritual entities who correspond to humans on a national level.
Deuteronomy 32.8 LXX (the Masoretic reads sons of Israel instead of angels of God):
When the most high divided the nations, as he dispersed the sons of Adam, he set up the borders of the nations according to the number of the angels of God.
Daniel 10.13, 20 NASB:
20 Then he said, “Do you understand why I came to you? But I shall now return to fight against the prince of Persia; so I am going forth, and behold, the prince of Greece is about to come.
There are spiritual entities who may influence human words and deeds on a personal level.
This influence may be direct (in the form of demonic possession) or indirect (in the form of tormenting a person until he or she yields).
1 Kings 22.19-23 NASB:
1 Chronicles 21.1 NASB:
Job 1.12 NASB:
The result of this permission includes attacks on his livestock and servants by Sabeans (1.15) and Chaldeans (1.17), as well as slightly more direct attacks on his children, such as fire from heaven (1.16) and a windstorm (1.18-19). After Job still does not curse God, in 2.6 the Lord gives Satan power over his health, the only proviso being that his life must be spared; in 2.7 the result is boils all over his body.
Ascension of Isaiah 5.14-15 (translation by R. H. Charles):
15. This, Beliar did to Isaiah through Belchira and Manasseh; for Sammael was very wrathful against Isaiah from the days of Hezekiah, king of Judah, on account of the things which he had seen regarding the Beloved.
Luke 22.31 NASB:
Luke 22.3-4 NASB:
John 13.27 NASB:
Acts 5.3 NASB:
2 Corinthians 11.13-15 NASB:
1 Peter 5.8-9 NASB:
There are spiritual entities who receive unmitigated credit for human words and deeds and for other life circumstances.
Mark 8.33 (= Matthew 16.23) NASB:
Notice that Jesus himself never even acknowledges Peter qua Peter; to hear Jesus say it, one might think that he was back in the wilderness being tempted by the devil. This credit even goes in reverse, when it is God getting the credit for acting through humans, as in Romans 16.20 NASB:
Your feet must belong to the Roman believers, yet it is God doing the crushing.
1 Corinthians 5.5 NASB:
Confer 1 Timothy 1.20. I do not think we ought to imagine Paul personally marching this poor person to stand before the very throne of Satan; rather, I think Paul expects this person to start suffering like Job did.
1 Thessalonians 2.17-18 NASB:
Members of my family, including my own parents, still say things like this. They are not claiming to have been granted an unwelcome and impromptu audience with the Prince of Darkness himself; rather, they are claiming that certain eventualities of life owe themselves to Satan.
Revelation 2.10 NASB:
I bet there will be jailers and local officials involved, too; yet it is the devil who is really casting believers into prison.
If we grant that 1 Corinthians 2.6-8 depicts demonic forces as having crucified Christ, but we also happen to think that humans physically drove in the nails, as it were, are we reading those humans into the text? Sure, but are we not reading humans (or life circumstances) into the Revelation 2.10 and 1 Thessalonians 2.17-18 and the rest, too?
If for some reason we prefer to think that these passages are only about Satan (or the devil), that he is personally and without earthly assistance imprisoning people and hindering Paul on his way to Thessalonica, then I suggest that we have perhaps made a prejudicial exegetical decision, however unconscious, that ancient writers are not allowed to credit demons alone when humans and ordinary life circumstances are involved (even though it happens all the time in certain circles even today).
Ben.
PS: Even if my argument here is valid, it does not necessarily mean that Paul had humans in mind in 1 Corinthians 2.6-8. It merely means that reading humans into the text is not automatically poor exegesis.