So if you shoot in one of the Auto Modes does it mean you're not a professional? The answer is a big and unequivocal "NO". I know many well known professional photographers that use some of the Auto Modes. The better question is how do these professionals utilize the Auto Modes? Using the Auto Modes as a starting point is the key. Let's break it down.
When do I use Auto White Balance? As you probably know, white balance is the way the camera interprets white. The color of white changes in different lightig situations and Auto White balance tries to automatically interpret this and apply the result to all colors. For example photos taken during the "golden hour" will have a natural yellow hue to them because the camera will interpret white with a slight yellow tint. The problem is that you may not want this interpretation because you want more control for artistic expression. Some photographers indicate Auto White Balance works perfectly well for them. They may want that yellow tint during the golden hour. After all that's why they shoot at that time. Others don't want the camera dictating anything. I personally use Auto White Balance only on landscapes or outdoor sports when the light is fairly constant, or I want the changes of hue to be part of the image (such as during the golden hour). However, if the day is over cast day or the shot is in the shade I will probably opt for the presets. But I never use Auto White Balance for studio Portraits. To make sure I get a natural skin color I will either shoot a color card or use an Expo Disc to get a custom white balance.
What about Aperture or Shutter Priority (Nikon terms for automatic modes)? I use both of these automatic modes. For me, Shutter priority is a must in shooting action sports. Since I shoot primarily high school sports I have to deal with going from evening to twilight, to under the lights. The venues sometimes do not have quality lighting so I have to deal with big changes in lighting conditions. These naturally affect exposure, but to get the action shot I have to shoot at a pretty fast shutter. Therefore, I make the shutter speed the constant and let the camera determine the aperture (and sometime the ISO). By shooting in an Auto Mode (Shutter Priority) I don't have to worry with constantly changing the other variables (aperture and ISO). My priority is getting the shot. If exposure is off a little I can change it in post.
I use Aperture Priority when I want to control the depth of field. This is primarily for outdoor portraits or macro photography. Yes I could use Manual Mode but I have found that the camera does a pretty good job of getting the exposure right and it can do it in incremental stops which I can't do with the internal meter. But if it doesn't nail the exposure the way I like I can always use Exposure Compensation to adjust to adjust shutter speed in 1/3 stop increments. This is my rule for outdoor portraits. I expose for the background using exposure compensation and then light the subject with speed lights using Pocketwizards and iTTL. This allows me to concentrate on depth of field while the camera does the rest. I tend to like darker backgrounds to place emphasis on the subject and I do this in camera with Exposure Compensation to slow the shutter and light the subject with speed lights.
Finally, is an automatic mode that some may not even know about and that's Automatic ISO (Nikon anyway). This allows your camera to automatically change the ISO based on the available light. I also use this for sports. Particularly if there is fairly low lighting conditions. As I mentioned earlier most of my outdoor sports are shot in conditions where the light changes quite a bit during the shoot. Rather than constantly changing this setting manually, or setting the camera to a very high ISO which will be needed as the light is diminished, I will let the camera make the changes as necessary. This mode is more of a requirement if you don't have a fast lens. You also need a camera that shoots well at high ISO settings.
So what about Manual Mode? Yes I shoot in manual mode. All of my studio portraits are shot in manual mode. Since I use studio strobes my shutter speed cannot be faster than 1/250, due to the sync speed. I will usually have a particular aperture in mind and try to keep my ISO around 100 to 400. So my lights are the real variables. I do use a light meter and adjust the strength of the lights until they match my camera settings. Certainly I could use an automatic mode, but I really want more control in this setting. Since I'm using a light meter it should be a more accurate reading than with my camera and that's very important in a studio setting.
So manual or automatic doesn't matter as long as you know the consequences and make the necessary adjustments.