The only negative aspect to eating avocados from a health perspective is that they are very dense with calories due to their high fat content. So it all comes down to matching your avocado consumption with your particular diet and caloric goals.
As unabashed avocado lover, I frequently get a craving for avocados that will only be quenched by eating one or two whole avocados a day for several days in a row, and have no qualms with indulging myself. There are certainly worse vices.
Avocados are definitely healthy for you, as they are packed with vitamins and nutrients and are considered to be one of the super foods, a list of the most nutrient dense and healthy foods available. But you can gain weight by eating too much avocado or any other high-fat foods such as olive oil, etc.
I would say that for the average person, half of an avocado a day is a better and more realistic portion then a whole one. But if you are physically active, you can easily get away with eating one or more without bloating up.
If you decide to limit yourself to a half an avocado, a great way to store the other half to eat the next day is with an avocado saver, which is a special kitchen tool designed to keep avocados fresh and green. Avocados are known to turn brown quickly after being cut, due to oxidation.