Too much fat doesn't cause artheriosclerosis, the real problem is oxidative stress. A ratio of too much polyunsaturated fats to saturated fats lead to more oxidation of fats. Saturated fats help in the utilisation of polyinsaturated fats, that include omega 3's.
Avocados are mainly monoinsaturated fats, which don't cause problems.
Another question: where do raw vegans get their omega 3's? There is a strong possibility that some people don't even have the enzymes required for the conversion of vegetal omega 3's to the ones required by the body, and thus depend on meat.