There are 14 defining characteristics of a fascist government, so i thought it might be useful to look at those with regard to this old chestnut about whether the Imperium is fascist.
1. Powerful and continuing expressions of nationalism
No. The is very little evidence in the sources of Nationalism being a part of local planteary structures or Imperial governance.
2. Disdain for the importance of human rights
Maybe. I don't think we much of an idea of what 'human rights' the Imperium recognises or allows so can't really assess this one.
3. Identification of enemies/scapegoats as a unifying cause
YES!!! Firmly part of the Imperium. Enemy without, enemy within, enemy beyond.
4. The supremacy of the military/avid militarism
Yes. The military is a massive part of the Imperium.
5. Rampant sexism
No. Women appear to be entirely equal in status whenever portrayed in the 40k sources.
6. A controlled mass media
Maybe. We really don't have much idea what mass media exists in the imperium. I suspect the Adeptus Terra will control it though!
7. Obsession with national security
See 1. Although security in general appears to be prevalent.
8. Religion and ruling elite tied together
No. Sure there's the Ministorum, and personal faith in the God-Emperor may be widespread, but...following Goge Vandire's Reign of Blood i think the separation of religion and state has been formly a part of the running of the Imperium.
The Imperial Cult was originally a part of the Administratum, but separated into the Ministorum.
9. Power of corporations protected
Maybe. there's no evidence of capitalist or corporate power in the Imperium.
10. Power of labor suppressed or eliminated
Yes. The masses appear to be oppressed.
11. Disdain and suppression of intellectuals and the arts
Yes. Ignorance is bliss.
12. Obsession with crime and punishment
Yes. Most things appear to be subject to arbitrary capital punishment...although what those things are is much less clear...
13. Rampant cronyism and corruption
Maybe. I don't think we have enough evidence to say for sure.
14. Fraudulent elections
No. As far as i'm aware, democracy and elections aren't a part of the Imperium.
Imperium fascist?
Yes = 5
Maybe = 4
No = 5
Hmmm.....so that didn't help at all!! D'oh!