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.
No, we all put our lines in different places, or even have a different graph.
However, if non-Catholic churches are inside the lines, then there's a much more substantial issue. Although I respect the Eastern Orthodox (as a generality - they have lemons just like every other church), there are serious theological differences between Orthodoxy and Catholicism. They are not interchangeable. (Here I'm addressing the thread subject, rather than you personally :-).