I am quite against vegan diets. Animal products have so many nutrients, and the macromolecular composition is much safer than plant products (fat is the safest macromolecule). While it's true that plants have a far superior antioxidant profile, they also have a lot of dangerous proteins that are specifically produce to interfere with our digestion, from taste to inhibition of nutrient absorption. They are also almost universally higher in carbohydrates, which leads to more oxidative damage.
There are plenty of arguments from evolution that also do not favor a vegan diet, but I won't begin to mention those. What is worth mentioning, however, is that a vegan diet is essentially impossible without supplementation due to a lack of vitamin B12 in plants. Several vitamins are also only fat-soluble, which makes it a little more difficult to get the most out of your meals, especially when your digestive enzymes are being inhibited by plant proteins commonly found in things like nuts, seeds, and legumes.
I would say, though, that plants have a necessary role in any diet. They are incredibly rich in many nutrients, and the antioxidants help to dampen the negative consequences of eating meat (these consequences are mostly present in modern meats because of how the animals are fed and processed. Feed crops absorb toxins from the environment (including pesticides and heavy metals) and are fed in massive quantities to the animals, which accumulate the toxins in addition to some of their own (vaccinations and antibiotics). Humans then eat the meat, and accumulate these toxins over many decades. This is not a detriment of the meat itself, but rather a consequence of being an apex predator in polluted land and sea).
A vegan diet for general health would probably lead to malnourishment unless one makes concessions, such as eating large quantities of legumes (take a careful look at this picture of a soybean; those are not hairs on the pods, but razor sharp spikes. Walk through a soybean field around the time of harvest and your legs will bleed: http://thenaturalfar...es/SoyBeans.jpg), excessive polyunsaturated vegetable oils (easily oxidized, quite bad for you), or egregious quantities of yeast (gotta get those B vitamins). For acne, I can't see it helping much either. In fact, because acne is a disease driven by a dysregulated immune system, a vegan diet might cause more damage in certain people because of all the antigenic foods (wheat, soy, peanuts, etc). If someone is getting acne because they are deficient in a particular vitamin, a vegan diet *could* help, but so too could any diet with that has plants as a part of it. Steamed meats are incredibly safe to eat; think about it - how many people have made the observation that their breakouts may be tied to unseasoned chicken, or white fish? And how many have made the observation that it's a plant food - citrus, strawberries, wheat, nightshades, nuts, soy, etc? The balance is shifted in favor of animal products.
But of course, as with all things, moderation; if all you eat is salami, you'll have a much higher chance of ending up with hypertension and colon cancer.