It seems that if you scratch the surface, almost any aspect of gardening can generate some controversy. On the question of leaves, controversy was apparently sparked by a post on the website of the National Wildlife Federation entitled “Why You Should Leave the Leaves”.
The NWF advocates using fallen leaves as a resource instead of bagging them to be carted away like trash:
Let leaves stay where they fall. They won’t hurt your lawn if you chop them with a mulching mower.
Rake leaves off the lawn to use as mulch in garden beds. For finer-textured mulch, shred them first.
Let leaf piles decompose; the resulting leaf mold can be used as a soil amendment to improve structure and water retention.
Keeping your leaves around enriches the soil, insulates plants, and helps insects and other wildlife to overwinter.