Two reasons. First of all, they honk. A lot. At everything. They honk at each other, they honk at people, they honk at pets, they honk at ducks, they honk while flying, while swimming, while walking, while fighting, while standing, and for no reason at all other than to say, "Hey, there's a goose here!"
And they're loud when they honk. Normally, this is just background noise of marginal concern, but when they start honking or fighting or whatnot at 5:30 am and waking you up, you'll get really annoyed really quick.
The bigger concern, though, is the excrement. It's been estimated that a single Canada goose produces between one half and one whole pound of shit per day. So you've got one goose cranking out that much, then multiply it by the typical 20+ geese that you have in a given flock. Geese usually arrive by early April and won't leave 'til October. We'll conservatively say 150 days. 150 days x 20 geese x 1 pound = 1.5 tons of goose shit in a given year. And I'm way underestimating those numbers.
That's a big mess. And it's toxic. It kills grass, releases viruses and bacteria, and stinks. It gets on your shoes, in your house, all over the place. Effectively, it will make areas near ponds unserviceable because there's no longer any place to walk and keep your shoes clean.
Oh, and where does all that shit come from? Geese basically do nothing but walk along, eat grass, honk, and shit. They will quickly and authoritatively destroy a lawn/yard/golf course. They rip up all the grass and shit all over what's left.
They are filthy, disgusting birds.
