Copyleft protects the freedom to use any materials that it covers wherever an individual may encounter them. It is inalienable and indivisible freedom. Weakening copyleft weakens this, and doing so should only be considered as a tactical last option.
Legal documents such as licences, however simple, can always have unintended consequences. Copyright law is complex and licences should always be drafted by lawyers familiar with the area. But this isn’t to say that alternative copyright licences should be motivated by lawyers or simply follow the faultlines of copyright law. They should be expressions of principle made rigorous and enforcible.
Software copyleft licences are tailored to the demands of writing and using software. But software is very different from other media covered by copyright, so this does not mean that other artifacts covered by copyright should have their own medium-specific licences. Culture is a dialogue, and much contemporary culture (including much contemporary art) is multi-media, or is adapted from or refers to work created in other media. A single-medium cultural licence would limit freedom of expression rather than protect the coherence of the medium.
It is possible to use non-copyleft “permissive” alternative copyright licences as a means of making irrational economic gifts of works to other individuals. The use of these gifts may support an individual’s freedom of speech. But this does not protect freedom of speech in general as the work they create using those resources need not be licenced to respect the freedom of its audience in return. Copyleft therefore protects freedom of speech more generally than permissive licencing.
Given all this, the licence that I believe should be used by individuals committed to artistic freedom of expression is a legally drafted general-purpose copyleft licence for cultural works. This excludes software licences (like the GPL), documentation licences (like the GFDL), and non-copyleft cultural works licences (like CC-BY and CC-NC-SA). It also, for reasons I will explain, excludes the FAL.