Overt vs Subtle

I have thought about this in bits and pieces over the past couple of years and thought I would try to put together and articulate it cohesively.  This idea has come up in connection with the education of children and with religion.  The question is that of danger.  What is more dangerous, the overtly wrong thing or the subtle, slightly, ballpark, almost right kind of teaching? 
A few examples might help clarify what I am getting at.  Would it be safer to send a young man or woman to a secular university or a nominally Christian one?  It's it safer for a child to listen to overtly anti-Christian music or subtley watered down, questionably religious music? The question really comes down to defenses.  Is an obvious enemy more dangerous or a secret enemy?
Think of the difficulties in either case.  With the overtly secular music or school, we know exactly who is the enemy and where the lines are drawn.  But with the subtle situation, the line is fuzzy, the black hats and white hats both look kind of gray.
With the overtly secular situation, one is deliberately walking into enemy territory.  But with the subtle situation, one does not know who exactly the enemy is.
I'm inclined to think that the overt situation is safer.  At least one knows where the lines are.  But of course there is still the question of influence.
Historically speaking, we have seen this exact situation in early middle age middle east.  When Islam and/or Roman Catholicism was overthrowing the middle east, the Orthodox Church chose Islamic rule over Roman Catholic, for the very reason I am discussing.  They understood the danger of subtlety.  We need to ask ourselves what we should do if we are ever in a similar situation.
And of course there is still the question of recognizing the subtleties and dealing with them as they arise. Is this a safe practice in which to engage?  Or should one avoid every subtle situation, if at all possible?  I would suppose it would depend somewhat on who is exposed and what is their level of maturity.  And then there is the question of multi generational influence. We must give consideration to how an overt exposure will affect the generations that follow us.
We can even take this back one step.  We should probably even consider the influence of acquaintances as well.  These are not enemies per se, but merely different from us.  Should we not think through the possible affects of exposure to these as well?