Tim Low's article "Australian acacias, weeds or useful trees?" criticizes aid and development agencies for planting and promoting agroforestry and forestry trees, like Australian acacias, across the world, highlighting evidence that several species have become problematic biological invaders. We propose an alternative to Low's blanket condemnation, emphasizing the importance of the regional socio-ecological context, taxon specificity, and participatory political process. We address flaws in Low's case that all wattles should always be judged dangerous, and ask who should make judgements - and on what basis - on whether people can diffuse plants across ecological barriers. Context-specific, socially debated and environmentally responsible diffusion of alien plants can amply satisfy the sustainable development goal of meeting the needs of the present while safeguarding those of the future.