For example, I am OK with high price/low quality IFS; my rationale for it being OK is that there is a downside (poor IFS rating, which affects reputation, route take-up, etc.) whereas exploiting the connecting passengers feature does not.
Fair. My rationale is that using connecting passengers doesn't affect the average player who isn't playing for valuation/rank. The strategy makes its own demand, and even on routes where there's competition I usually have 0% (or maybe 1%) market share since my prices are usually ~3x default. And if players are playing for rank but still demanding realism, it feels like they're asking who can make the least realistic realistic airline, since all those unrealistic tricks (scam IFS, 660Y 744s, $7 wages etc) are going to increase your profits and rank. I just don't buy that as an argument and figure that as long as I'm not preventing folks from making their own fun airlines, it's fine.
This is also part of the reason I chose to operate in Saudi Arabia - when I joined 5 years after the world started there were no other airlines there, so figured I wasn't unreasonably taking market share from anyone in the setup.
Never going to advocate (for example) for the kind of spamlines that operate with $1 fares on routes, though, since that directly affects players who want to operate them. Guess we all have different lines.