I don’t think that it should be banned if the R isomer can be synthesised and proven to be purely the R and not the S isomer. Thalidomide is still used to treat patients for certain cancers and some other conditions successfully and it is also FDA approved for cancer treatment.
I don’t think a complete ban on enantiomers is ideal – especially if one is particularly useful. Synthesis techniques which allow for enantiomeric control are quite well developed nowadays, alongside separation techniques that allow for obtaining only one enantiomer in high purity, and there is more regulation in place to make sure that only the useful enantiomer is present in medicines.
Thie issue with enantiomers was the attitude taken by the pharmaceutical industry – prior to thalidomide, there wasn’t much concern about leaving both enantiomers in the medicine – if you had a 50-50 split you’d just increase the total amount of drug in the dose, since the other half was believed to have no or minimal effects whatsoever, and would effectively just take up space. Less processing means that you can have faster production and less costs, and have higher profits (there’s quite a few questions that one can ask relating to these ideas, such as when does it become profitable to cure a disease which only a few people suffer from)
I agree with Rose and Thomas; it shouldn’t be banned providing that the R isomer can be isolated – whether it be via synthetic means, subsequent purification steps or both. I spent some time working in pharmaceuticals and purification methods are very advanced now such that enantiomers can be separated. Following on from this the toxic effects of each have to be documented so a decision can be made as to whether the final product can be a mixture of both, one (or none – go for another molecule instead).