Vegans/Vegetarians are no weaker than meat eaters AS LONG AS THEY DO IT RIGHT. People say they're weaker for many reasons, but this is the reason I've found to be the most common -
A lot of meat eaters will 'try' a vegetarian/vegan diet for a few days. Thing is, most people who eat meat haven't a clue how to eat a balanced diet as a vegetarian, and just eat salads, bread, and french fries, while completely ignoring common vegetarian protein staples (tofu, tempeh, seitan beans, nuts, whole grains, legumes). What many people fail to do is balance and combine their proteins correctly, and they're left feeling weak and tired. By the end, they think 'There's no possible way vegetarians and vegans can get enough protein and be healthy'. I've seen this happen a lot.
Vegans don't have higher risk of joint problems, as long as they get their calcium. Today, there is a mass misconception about how to get calcium, mainly caused by the mass advertising campaign put out their by the factory dairy industry. Thing is, milk is NOT the only way. Green, leafy vegetables (the darker the better) are packed full of calcium, as well as many whole grains (a cup of quinoa has more calcium than a whole quart of milk). Many fruits and veggies contain even small amounts of calcium, as well as other beneficial vitamins and minerals, so if you eat a lot of them (with at least special attention to eat the leafy greens at least once a day) you'll be fine and have stronger bones than most meat eaters.
And yes, vegetarians and vegans have a significantly lower risk of heart disease. Americans today eat more meat than any other developed nations, and that is wracking havoc on our bodies. Red meat is especially artery clogging, especially with the way it is produced in America (cows are fed corn instead of grass, and they become fatter, so the meat is 'marbled' with fat that is terrible for us). Most people ignore the recommendation that we're not supposed to eat red meat more than once a week. Meat CAN be a part of a healthy and rounded diet, as long as it's hormone free, unprocessed, and organic, and we mind the portion sizes and be sure to eat our whole grains and veggies.