Objective Accountability or Subjective Expression
Once one has accepted the basic moral principle, the task of moral deliberation truly begins as one is confronted with the task of living one's own individual life, of taking personal responsibility for one's decisions and practices. This is the task of living constantly mindful of one's basic orientation toward life expressed in basic principles or attitudes, without a set of rules that make one's decisions for one. This means that your decision, for example, to hunt, as long as it is consistent with or a personal expression of the basic attitude, can be correct for you without necessarily being the correct decision for me, even if we both adopt the same basic attitude. The moral life is a way, not the simple application of a set of moral rules. Many paths can diverge from one another within the common pursuit of this way.
The contrast here is between objective moral rules -- those that are binding on all people and to which one person can hold another accountable -- versus subjective moral rules -- those chosen by the actor as their personal expression of how they value their moral commitments. The distinction is not unique to Evans and Schweitzer, nor is the judgment that objective rules are slavish while subjective ones allow for deep expression of oneself.
Evans' aversion to objective rules seems to me to be based on caricaturing the objective-rules position. He attributes two characteristics to it -- that it's externally imposed, and fully worked-out. That enables him to portray objective-rules-followers as slaves, forced to follow whatever the moral code demands, without thinking about their own relationship to it. This portrayal of objective rules is perhaps a lingering legacy of traditional Christianity, in which the rules flowed from God to obedient humans (with a paradigmatic positive expression in Divine Command Theory and a paradigmatic negative one in the New Testament's portrayal of the Pharisees and Mosaic law).
But this external command view of objective rules is far from the only way they can be conceived. Objective though they might be, the rules of morality are always a work in progress. They always require further thought, debate over the nature and relative strength of values, etc. to be applied to particular situations and new circumstances. There is rarely "simple application" here, but there is a requirement to be "constantly mindful."
What of the subjective-rules approach? In its extreme existentialist form (and Evans seems to have some sympathies for existentialism), it threatens to slide into relativism. Anything is permissible, even obligatory, as long as you're willing to take responsibility for it. But at this point the moral content of the whole enterprise seems to dissolve -- how can we differentiate this approach from plain enlightened egoism? And what does "taking responsibility" consist in, beyond a personal attitude in one's own head toward one's actions (since others' attempts to hold one accountable would either be impermissible because they involve imposing one person's ethical rules on another, or morally neutral because the actor has accepted the risk of the holding-accountable as a foreseeable consequence).
The ultimate problem with the subjective-rules approach, I think, is that it's asocial. You are the only possible arbiter of your own actions, because only you can know how deeply and seriously you're thinking about their grounding. Other people are at most suggestive models -- they can't directly hold you responsible for making the wrong choice because what choice is right for them has no necessary bearing on what choice is right for you, even in identical circumstances. For someone who builds his environmental ethic on the importance of participation in the natural community, Evans (and Schweitzer) seems awfully reluctant to substantially engage in the human community. Indeed, it seems to me that decision-making, and taking responsibility for one's decisions, only make sense when the rules one is seeking to be guided by are objective and hence available for others' scrutiny and judgment.
(This is not to say that there is no room in life for a subjective-rules approach -- subjective rules have free rein anywhere in life that objective ethical rules do not prescribe a certain course of action, or where the objective importance of the ability to shape one's own lifestyle is the dominates other considerations (one of the great attractions of the liberal tradition of political philosophy is the emphasis it puts on the importance of carving out a substantial sphere of life for subjective expression). But subjective rules fill in where objective ones leave off and are always vulnerable to being trumped by them, rather than being an alternative to them.)
While this problem with subjective rules is common in many moral arguments, it also goes to the heart of the problems I have with Evans' theory. He claims to base it in objective facts -- the biological interdependence of all life (here treading closer than he wants to admit to the naturalistic fallacy) and the act of participation in that interdependence. But when everything is worked out, he ends up resting the justification for hunting and fishing on subjective attitudes of the hunter or fisher. Hunting or fishing becomes about what the quarry means to me -- not what the quarry means to itself.