In fact, I do not recall ever reading material that confirms your characterization of Silvanus and his faith, nor the laws of his faith.
Then you mustn't have read much about it at all. The followers of Silvanus are known for vigorously and VIOLENTLY defending their home turf.
Nor do I think druidic attitude towards outsiders is as uniform as you describe.
The church of Sylvanus is exremely diverse when it comes to moral outlooks because Silvanus doesn't care about morality at all as long as your promote the protection of untamed wilderness. We are talking about a Druidic cult of Silvanus druids here, not of any other deity.
druidic magic is not in and of itself divine in nature
Not only is this false in general, it's especially false in a circle of druids who get their spells from Silvanus.
it is not common for a god to immediately thwart magic that is cast in a way that contradicts the tenets of their faith
False, again. The only deities that would roll with that are chaotic deities, like Lolth who allowed one of her clerics to heal Drizzt in one of the books. And then she punished the cleric, but that's Lolth being insane.
