The town of Jefferson changed a great deal during the timeline of the story. It is Emily and her family that do not change. Faulkner was always critical of the South's view of itself. In this case the condemnation would fall upon the Greirsons more than the town of Jefferson.
The key line is in how Emily clings to the dead body of her father. Faulkner says that he cling to what enslaves us. She was under her father's thumb her whole life. She was reliving that moment of impending abandonment with Homer.
The town were cruel on-lookers, fiendish gossips and rooted for her downfall, but there was nothing they could have done to impede this madness. I say not guilty.
The druggist should not have sold Emily the poison, just as a bartender should not sell more liquor to a drunk man who intends to drive home. In doing that, the druggist does bear some responsibility. But responsibility differs from complicity, in that the latter involves “aiding and abetting” a criminal act with intentionality. The fact is, the druggist was too weak to say no to the woman, which brings us to the issue of the culture of the town. Your question raises the issue of to what extent any community is responsible for the evil acts of its members. Certainly kindness, understanding, and compassion, as well as a good father and a society that did not disparage single women might have resulted in Emily not seeking out Homer, not needing him to the extent that she did, and the town not being afraid of confronting her when it needed to. Yet, in the long run Emily is responsible for her own actions: she planned this murder very carefully, after all, and showed herself a rather strong although deeply wrong woman in doing so.
Certainly the whole town has enabled Miss Emily's actions by playing to her disillusionment. If Miss Emily does indeed represent the Old South and its stagnation while the town represents the New South, Homer is a victim of the of the South's obsession with tradition and heritage. Yet, the town does not acquiesce to Homer's murder and is quite repelled by the discovery. Even though the townspeople are not endeared to Homer because he is a Yankee, it would be a stretch to conclude that the town wanted Homer dead.