The fast food salads are a gesture towards offering healthier food but they are far inferior to salads you would make yourself. Usually the lettuce is limp and the tomato the merest sliver. If you have a heavy dollop of slaw or mayonnaise on top of the salad, you're undoing a lot of any good. Yes, a salad is better than a heap of fries, but look at it objectively. Is it crisp and free of oils and other sauce?
Depending on the fast food restaurant and the salad, fast food salads can be healthy. At least, some are. However, some aren’t. Dousing any salad in thick creamy, calorie-laden dressing would totally damage the healthiness of a salad. Also, putting fried chicken instead of grilled chicken will add cholesterol and fat to a salad. Some of the fast food salads that contain green, leafy lettuce with grilled chicken would probably be considered healthy by many dieticians.
The extras that are added onto a salad like candied pecans and blue cheese take the healthiness out of a salad. They would be comparable to the Big Mac and large friends. If you want to order a healthy salad from a fast food restaurant, keep it simple with grilled chicken and light dressing.