My nethods are always intended to be used as methods ($obj->method(...)) and non-methods are always intended to be used as functions (class::function(...)). Method invocations rely on the first parameter being an object of the required type in order to function properly and to make sense. Yes, an end user can do whatever he/she wants (this is Perl, after all), but it won't work correctly in many cases, since additional methods and properties will likely be accessed in a method. For methods, my understanding is that $obj->method(...) and class::method($obj, ...) (assuming $obj is of type class) are functionally identical. Feel free to correct me if I am wrong.

In almost all cases, my methods and fuctions all have specific parameters that they are expecting (i.e., nothing, two scalars, a scalar followed by an array, a hash, etc.). So how is this dangerous?

I am aware that some Perl functions are flexible to accept multiple types of parameters and I have left off prototypes when I have created such functions, but I generally don't create functions like that. If I want to create such functions, then I usually use a hash/hashref as the last parameter and pull key/value pairs as needed.