Here are a couple of answers to questions I've seen brought up on SC.
Q: Why Sunni sources?
A: To shatter the illusion that the Imamah of the Twelve can be proven through Sunni sources. It simply cannot be proven.
Q: Allah will judge others who have not accepted Islam for sticking to their own sources. Can’t any non-Muslim say this?
A: A Christian will not be able to use a corrupted Bible in his defence on the Day of Judgement. No such effort has been put to preserving the words of a prophet as the Sunni hadith system, and whoever believes otherwise is delusional.
Q: Why not debate on another matter?
A: I don't mind debating on other issues. However, the debate has been issued over this specific one right now. If the mods do not endorse anyone to debate this issue, it should be well known that the mods do not believe that Shias can prove this point.
Q: How about debating the attributes of Allah?
A: That debate is not exclusive to Sunnis and Shias, and Sunnis disagree amongst themselves on how the attributes should be understood. If I was to be convinced by the Shia debater, I would still become an Ash'ari Sunni.
Q: Why not come to Shiachat, make a thread, and debate whomever you want?
A: Last time I debated Wasil, he started doing so bad that Shias called it a set-up, and started saying that the debate was rigged. I am not making that mistake again. Two moderators will have to endorse the debate. I am not wasting my time debating "fake Shias". Once again, I am hoping for a good opponent that provides strong arguments.