Not a good idea...
If large numbers of users were to deploy this, it would be bad news for web hosting providers and web site owners. Using SSL for everything will add significant extra processing demands in places where it is not necessary.
The bandwidth is irrelevant, encrypted data does not take up much more space than raw data. The important thing is the processing overhead. To protect the privacy of communications, we rely on modern encryption technology such as SSL without thinking about the considerable maths that needs to be performed.
More CPU power = more energy used = more heat dissipation.
This would have serious implications in a data centre with hundreds of servers hosting thousands of web sites. To serve the same number of requests, more physical computers will be required, more electricity will be consumed and more heat will have to be removed.
The bottom line is, potential massive impact on the environment, not to mention budget worries for businesses in today's economic climate.
The intentions behind this little tool are good, I wholly advocate privacy and the right to protect it. However, these concepts must be applied appropriately. It seems they might not have fully thought through the implications of such a blanket approach.
The tool should provide users with the ability to 'prefer SSL' in specific cases where they would like the additional peace of mind. It should make these choices as granular as possible, for example by targeting certain pages; targeting only pages where information is submitted (forms) and giving the option to include or not include images and other multimedia.