Aren't we all?
From my experience, goose behavior towards other types of poultry can be unpredictable because it may be multifactorial: I believe personality is a combination of genetics, how the birds are raised, and maybe unidentified influences (the nurture vs. nature debate). For example, some breeds, generally speaking, seem to be more accepting of other kinds of fowl - Pilgrims and Americans are reputed to be "nicer" to chickens and ducks, so the
potential for them to get along with chickens and ducks may be greater than certain other breeds...but there will likely still be geese of those breeds that won't get along with chickens or ducks. Conversely, there may be Chinese or Toulouse geese who are great with chicken and ducks, despite a reputation (generalizing) for being less accepting.
In short, even choosing a docile breed may not guarantee they'll peacefully coexist with chickens and ducks. Further, I don't think geese are any more effective as deterrents when they're solo birds attached to a flock of chickens or group of ducks. What you
can control, however, is how you raise them (hopefully, as happy geese with a companion of their own species to be a deterrent team) and how you handle conflicts that may arise.
With regard to cases where geese raised with other types of poultry became aggressive, the situations I've heard of involved ganders during breeding season - normal behavior. Do I think it's possible geese raised with chickens or ducks could unexpectedly experience conflict at some point? Yes...especially since they're different species and they, effectively, don't "speak the same language", so misunderstandings can occur.
I recommend that if you pursue getting deterrent geese, you familiarize yourself with typical and atypical goose behaviors - e.g., "noodling" can look scary, but it's usually normal goose behavior - and proven methods of addressing unwanted behaviors so you can nip any problems in the bud and avoid injuries or having to rehome birds.