I just started to think about a Cleric character/protagonist and the diversity of imperial creed and then I came to this.
Who and why has to be celibate?
Sororitas because they are nuns and 'married' to the Emperor?
AdMech because flesh is weak and they remove the proper parts first?
Astartes because the are so rebuid and conditioned that they lack any sex-drive?
All clerics?
Some clerics?
Does it depend on the rank they aim for, the certain one of the sub-cult they are part of?
Is it a vow they can take on by choice?