The term of 'human dignity' is not an actual and verifiable concept, but a totally subjective and metaphysical one. It means that human dignity is not the primal concern for scientists - actually, it is not their business. On the other hand, there is strong belief among the popular, especially within the religious camp, that the human dignity should be taken under no circumstances. That's why it is so difficult to dialogue between science and religion.
As we are entering into new era led and controlled by genetics, it is increasingly observed that genetic researchers easily trespass on the human dignity, i.e., by naming the pre-embryo as a lump of cells not a human being.
The reason why we have to limit genetic interventions for the improvement of genes is because of a danger of eugenics. In that sense, we also need to consider that it is very difficult to discern gene therapy and gene enhancement, because the former can easily fit in with negative eugenics and the latter with positive eugenics in actual fact. The human desire to have 'perfect baby' will go on well with genetic interventions, and bring into new gene-classist society in no distance future.
We hope that genetics will not serve as a type of genetic Procrustean bed against which individuals will be measured; instead, it serves as the giver of benefits for all. For this end to be fulfilled, we have to make a consensus of what is human dignity and from what stage in the human developments he/she holds his/her whole personhood as a meaningful life. If we are wise enough, we can adjust our desire to intervene in our offspring's genes as well as our own to the evolutionary process of nature.