I don't know about this. Weakness of will is an individual character trait which could apply to ethical persons just as easily to unethical persons. A person may have a terrible smoking habit but would never advocate anyone else smoking. There are lots of impersonal preferences which conflict with personal perferences. Weakness of will is perhaps the antithesis of courage.
Courage is a form of endurance.
This is a big perhaps. When the phrase 'weakness of will' is used, it has really nothing to do with ethics. It is not my will be done, but 'Thine Will Be Done'. Reducing personal consumption is about conserving income, keeping the earth looking pleasant and tidy, and many other sort of basicallly good traits and habits. This is the stuff of good habits itself, but I think environmental ethics is more comprehensive, and universal in the sense of a social form of common exercise.