Doesn’t shredding all of your leaves result in possibly shredding next year's generation of butterflies and moths?

It is certainly true that many caterpillars or pupae (whether in a cocoon or chrysalis) overwinter attached to a stem of the host tree or may drop down in the leaf litter. While mulch mowing will, as you point out, cause casualties for creatures clinging to fallen leaves that are then shredded, it is also clear that overwintering butterflies and moths have little chance of survival if the leaves they happen to be attached to are raked up, piled at the curb, vacuumed up and carted away to a commercial composting facility.

As a general observation, since grass does not survive under cover of whole leaves, most homeowners and property managers remove them every fall.  In this context, mulch mowing is the most environmentally-friendly way to enable people to maintain their lawns and to better utilize rather than remove leaves from their property.

It would definitely be a good outcome if more people will think twice about the needs of the tiger swallowtail, the crecopia, and other gorgeous and important lepidopterans, and how they can support these creatures by providing their specific native host plants. In the fall, the clean-up strategy should allow for at least some whole leaf litter to remain untouched around the base of host plants in landscape beds, yard margins, or wooded areas, wherever feasible on their property, thus increasing the odds of survival for these overwintering insects.

Here is an interesting article (also podcast) from 'A Way To Garden' website which discusses various techniques to use during Fall cleanup to protect and encourage wildlife (esp. insects and birds): A saner approach to fall cleanup, with the Habitat Network’s Rhiannon Crain (pdf). OR listen to the podcast.