Dylanrockin

Let's take a look at some unhealthy factors that can lead to an association in the first place:

Constant exposition to and fascination with characters from a very young age, combined with too much imagination, hours spend in front of the tv/comics/media in general, high sensitivity, and preexisting issues (genetic or otherwise), as well as the nature of character depiction especially in anime/manga and some styles of comics or fantasy novels where human features are extremely exaggerated and may, in turn, trigger exaggerated responses in the brain (debatable, but looks like it's an addiction factor - no matter whether addiction is a brain disease or the manifestation of a pre-existing problem). This, especially if combined with  socialization problems of relatability with real humans, may enforce a fake bond with a fake person due to overstimulation and the inability of children to differentiate between real people and imaginary people at certain ages. Suffice to say, overstimulation alone can reinforce this in older ages too due to the numbing of normal responses, especially if the person has already got a history of exposition to said material. Unhealthy escapism (escapism in general is an unhealthy approach though, one might say). Lack of varied human contact, self-isolation, lack of proper socialization (or too little socialization) during childhood.

Also, there is an ongoing debate whether internet and explicit material addiction falls under the brain disease category, and whether some things are more addicting than others - some say this is not the case because an addiction cannot be acquired if there is no preexisting condition. Others say that this can still happen just to a lesser degree and variety. If the latter is true, then the aforementioned character depictions "overstimulate" dopamine and can have an adverse effect on the brain (especially a younger one), not to mention the absolute multitude of mental problems this can cause. This of course, makes the association pathological.
 

So to answer the question...it's difficult to discern where that point is, since even the association itself might not be that healthy in the first place.
Or at least, it may reach unhealthy levels after repeated behavior.