Extraterrestrials are not likely to visit Earth, but not necessarily because they don't exist. The problem arises with the use of the terms "extraterrestrial" and "visit". The term "extraterrestrial" specifically refers to a thing or life-form that originates or exists beyond Earth's atmosphere. The term "visit" inherently refers to the concept of "travel", which means (although not exclusively so) to go from one point to another via MOVEMENT. And while a visitor from another planet could technically be thought of as an extraterrestrial, this, generally speaking, assumes that such a life-form TRAVELED (or MOVED) from another (extraterrestrial) place.
The assumption these terms make is that an extraterrestrial life form has to move through space (and consequently time) in order to visit Earth. After all, this is how WE interact with the immediate world around us. However, because of the immense distances found between "extraterrestrial" places, any life-form with sufficient enough knowledge to "travel" throughout the universe would likely be accessing the fabric of reality in an entirely different and unfamiliar way.
Various fields in mathematics tell us that there are far more dimensions than the 4 we consciously experience (that of length, width, depth, and time). Many of these "additional" dimensions bend space and time so that a thing can exist in two or more places instantaneously. Some even hint at states of timelessness (as does both ancient and contemporary spiritual sources). The existence and nature of these dimensions is not fully understood and leave room for many possibilities.
That being said, a life-form with the ability to access a large range of dimensions would be far more likely to visit Earth. As such, what we traditionally think of as "extraterrestrials" should more aptly be thought of as "transdimensionals", or life-forms with the ability to cross through and/or exist in multiple dimensions.
Long Side Note: By default, we typically extend our immediate experience of a thing into realms beyond our immediate, or even extended experiences as a way of relating to the unknown. While this may create a point at which to begin further investigation, it can also stifle our perceptions if left untended. The problem is we make assumptions about the unknown (like the one above) based on an extension of LIMITED relatability. The average 1st world citizen engages in far more self-serving, short-term activities than they do in seeking unfamiliar, unrelatable experiences, yet so much of our daily lives are directly shaped by assumptions about these unfamiliar experiences. While certain individuals may escape this dynamic to varying degrees, we are collectively defined by this tendency. And as guilty as I am of these same things, spending a morning in line at Starbucks, finding the perfect app, and tweaking the layout of umpteen different social profiles does nothing to extend our understanding of things just beyond the threshold of human experience, and only serve to increasingly saturate our lives with that which is already familiar. A young race should not specialize in pursuing its own comfort and pleasure, but rather seek to broaden its exploration of the mysteries surrounding its collective origin.