I appreciate your conviction. To address each of your points:

I want EVERYONE to be happy, content, and finds ways to spread joy. However, the park belongs to everyone and not everyone appreciates the trees being "livened" up. I think they are more beautiful left alone, in all their frozen glory. 

Making hats for the homeless would absolutely, undeniably be more productive than making sweaters for the trees.

Those "unnatural city trees" are the direct descendants of the birch trees that were in that spot before Anchorage existed. They may have shifted a bit during the earthquake, but they're the same ones. 

Let's not forget that real art goes in museums. Even a Van Gogh would be stolen or vandalized if left out overnight. These outdoor exhibits are bound to offend people and prompt "cleanup" to restore the landscape to its former condition. Why not put sweaters on trees in your own yard instead?