This doesn't seem to be dark arts to me. The use of graphs as a persuasive element seems to use the fact that graphs are visual and striking and so can overcome our cognitive defenses which prevent updating. This may connected to why graphs are such a useful mode of communication. Similarly, starting people off where they feel good about themselves may simply reduce the level which they feel a need to defend their beliefs as part of themselves.

So I don't see either of these as Dark Arts per se.

I am puzzled by the downvotes. I suspect that they may be coming from the title of the post which is unfortunate because people can read the link to see that the relevant methods worked on people across the political spectrum about issues they were otherwise unwilling to examine.