I always feel uneasy when there's talk of using guilt to persuade parents into using cotton - there are some who for one reason or another just cannot cope with them, and many feel guilty enough about it already (isn't being a parent one long guilt trip anyway?!). Better I think to dispel some of the myths surrounding cotton - eg more nappy rash, expensive, loads of soaking, smelly, hard work etc etc and point out that they can (although not always) work out a lot cheaper, can actually reduce nappy rash and eczema and can be sold second-hand so you get back at least some of your investment! Plus it costs around �30 for a council to dispose of one baby's disposables, so a lot of councils refund this to cloth users. There are also more eco-friendly disposables which are biodegradable or are made using fewer chemicals than standard disposables, so there's a greener choice for those who can't use cloth.
As to whether or not cloth is truly more eco-friendly - there is an argument that cloth wastes more water, energy and chemicals in the washing and soaking process. A study into the environmental footprint of both types of nappy is being conducted at the moment; as far as I know the report hasn't been published yet.