The wording is "do my best to do my duty" etc. Open to intepretation what one person's best is (it's never exactly the same as someone else's) and what constitutes duty. Simple. I didn't study philosophy for nothing, you know
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The Cubs make say the promise as is. My opinion is that it's almost (but not quite) worthless, as eight year olds aren't old enough to make promises, know who their god is (if any!) or what duty is. Most of my cubs are from families who have no religion (by the way).
I try to instill in them respect for self, respect for others, and respect for their surroundings. With that as grounding and a decent education in the rest of their lives, they should be fine.
The Beaver promise is almost perfect. It would be just right for everyone if the last four words were removed:
I promise to do my best to be kind and helpful and to love god.
They could change "love god" to "try to be good", which is what it really means, but that would be tautologous (see previous words of promise) as well as a bit yuck.