Sorry Eagle, you're wrong on this. League is team competition, and you're ethically obligated to TRY to SCORE your best. Without everyone doing their best to score, the integrity of the league disappears. What's ironic is that you'd never get away with scoring less than your best in anything other than handicap. Try your best using just plastic in a scratch league, and the USBC would be the least of your worries. Your teammates would perform their own justice on you at some point early in the season.
If you're bent on trying your best while intentionally using inferior equipment, have at it during open play practice. There is a time and place for everything.
The problem with your argument is that you are bringing other variables into the equation. Simply put, there is NO USBC rule that is being violated as described by the OP. In addition, many of the people that disagree with this also keep bringing other variables into the equation.
Is there a rule against this...NO.
Oh, but if it's a handicap league, then you are gaining an advantage and "someone" is getting cheated...um, what rule is being violated? None. Just another variable to try to justify someone's misguided belief, typically not based in any FACT.
Oh, but if it's a scratch league, then you wouldn't think of doing it...um, why not? Again, another unrelated variable with no bearing on any rule. What your teammates think (or someone's belief about ethical concerns) has nothing to do with the lack of a rule violation.
Consider this...
1. New league bowler with 2 years of experience has thrown urethane for his whole career. His buddy tells him a reactive ball would give him 30+ pins/gm. He decides not to get one because he can't afford it.
2. Ex-touring pro hasn't bowled in 15 years, joins a local league and throws the only ball he kept, an old urethane ball. Even though he has connections, he chooses not to upgrade his equipment.
3. Accomplished bowler with 20+ balls in his arsenal joins a league and decides he wants to throw urethane. He walks in every week with only his urethane ball.
None of the above bowlers uses a reactive ball for the league. However, all of them choose to upgrade over the summer and bowl a few tournaments using the average from the "urethane" league. Who was sandbagging?
The answer is simple...no one was sandbagging.
You are only obligated to do your best with the ball in your hand. Are you sandbagging if you bring the wrong bag to league and have only dry-lane equipment for a 1st shift heavy oil league? If teammates, coaches, and other high-level bowlers tell you that you'd pick up 30+ pins/game if you bought "x" ball and you CHOOSE not to, are you sandbagging?
No one can make any bowler throw any ball, whether it would work better or not. If you would like to bring in the many variables why you disagree that is fine, but open up a new topic because those variables have nothing to do with this topic.