Whether a thing can keep going without consuming what it depends on. Sustainability is a question about time, not about virtue.
Latin sustinere (to hold up, to sustain, to endure), from sub (under, up) + tenere (to hold); whether a thing can keep going was always a question about holding, not about the intentions behind it.
Whether a thing can keep going without consuming what it depends on. A question about time and holding capacity, not a claim about virtue.