The motive for the smear campaign
Metcalf later published a pastebin of a Skype conversation between the XC team and the SDC team. A merge was under discussion. https://bitcointalk.org/index.php?topic=829576.msg9422912#msg9422912
As can be seen, the meeting was very positive. However that sentiment changed in the week following it. Some SDC holders were opposed to the merge and managed to dissuade the SDC dev team from it.
This resistance to collaborating with XC extended to the Blocknet, when they successfully persudaded the SDC team to withdraw from the Blocknet prior to launching their smear campaign against it.
In retrospect the smear campaign appears to be an attempt to destroy Dan, XC, and the Blocknet in the hope of attracting users to SDC, a coin with legitimate anonymity features and thus a direct competitor.