If you think something in a parish is dangerous, as opposed to just "not ideal," then you have an obligation in conscience to go somewhere else.
I think by "fine line" I was specifically referring to liturgical practices.
Examples of what would be dangerous IMO:
Priests changing the words (ad-libbing)at Mass, whether essential or not because this makes a mockery in either case.
Homilies bordering on and/or overtly heretical
For children, seeing bad example in the worship accorded to Our Lord in the Eucharist
Examples of what is not dangerous, but not ideal:
Bad music
Bland homilies
Lack of parish community
The fine line lies in what one considers to be dangerous or not. Not all will necessarily agree with my categorization above.