As with most dietary questions, vegans are split on the issue of dairy products--not so much on the question of whether or not they are acceptable, but instead for what reasons they should not be consumed.
All vegans (or at least true vegans) abstain from consuming dairy products. Some do so for nutritional reasons; others abstain for ethical reasons. Those who do it for nutritional reasons cite a range of health problems related to the consumption of dairy products, including high cholesterol. Many also have a problem digesting lactose or have a blood-iron or diabetic problem related to milk protein, casein. In addition to this, milk and cheese often contain small portions of undesirable hormones that are added to dairy cow feeds to increase production.
Those who abstain from consuming dairy products for ethical reasons also have a range of reasons for doing so.
Some cite the poor treatment of dairy cows as a main reason for not consuming milk and cheese. They note that dairy cows are forced to become pregnant once each year to maintain a constantly high yield of milk. They are also fed numerous steroids to increase production.
Others who abstain for ethical reasons often cite the maltreatment of dairy cow offspring. They note that calves are not allowed to spend time with or suckle from the mother, but instead are prematurely removed to be reared for either veal production, beef production, or as replacement dairy cows.
The calves selected for "veal" production are often forced to live in crates so tiny that they cannot turn around. They must face in one direction; they cannot groom themselves; and they are fed hormone-laden feed until they are sent off to be slaughtered.
If you are a prospective vegan, you may want to take some time now to think about what is best for you. Ask yourself whether you wanted to become a vegan for ethical reasons, dietary reasons, or both. And from there, determine whether or not these arguments were strong enough to compel you to do so.
Either way, you should emerge with a stronger viewpoint and a better understanding of what you do and do not want.