Positive and negative formulations of the golden rule. Rules like this can divided into two forms: 'positive' and 'negative'. Generally, the positive formulation follows a form something like "treat others the way you want to be treated." The negative formulation says "don't treat others the way you don't want to be treated," which seems to be more an exhortation to 'live and let live', instead of an exhortation to actively go out and make other people's lives better.

The forms quoted previously from Christian, Islamic, and Taoist sources are 'positive' forms. The others are negative forms. (curiously, these are the newest religions in the list)

Which is better? Proponents of the 'positive' formulation like myself argue that there's no love in merely avoiding harming others. William James once said that being invisible is worse than torture, and by the same token, merely avoiding the active harming of others isn't far enough; nor does practising it result in a just world - it gives you an uncaring world (like a mighty capitalist dystopia) where, contrary to truth, every man considers himself an island.
People who prefer the negative formulation tend to argue that, being human, there's no way we could ever hope to actually positively love everyone all the time, and anyone who tries to is a hypocrite. So we should stick with something realistic, which is avoiding harming others.

Personally, I don't think attainability is the point.