Tax evasion is lying about what you owe; tax avoidance is legally minimizing it — a distinction the law draws clearly, though reason finds it less satisfying than the law does. The question is not only whether the behavior is legal but whether it is consistent with what you claim to believe about the common life taxes fund. Those who most benefit from the infrastructure of civilization and most aggressively avoid contributing to it have not resolved this question by finding a loophole.
Each step builds on the last.