Skeptics aren't suggesting that that the apostles and others died for their beliefs. They are asking Christians to believe that the apostles and others died for their lies, for something they KNEW to not be true; because they said they were eye-witnesses.
Nothing establishes a new movement like a few martyrs. Generously assuming that legends about their deaths are historical, all we have is a tale as old as religion. People killing and dying for their faith. Are to presume every visionary or prophet or who was killed must have been divinely moved?
First we have Paul, like DisiJW just said Paul claimed only to have been fated, chosen before birth to be a visionary.
But when he who had set me apart before I was born, and who called me by his grace, was pleased to reveal his Son to me, in order that I might preach him among the Gentiles…
He also claimed to have had visions of the layers of heaven (as was commonly believed see Enoch) and heard secret unspeakable things that he kept to himself. (2Cor12)
After years of preaching Paul goes to Jerusalem, to get to know a Cephus. More than a decade later he returned to Jerusalem again, met with Cephus, a John and a James. He did not mention anything about "eyewitnesses" only that they 'were esteemed to be pillars' in their church. The gospels had not yet been created so as to give these names a significance beyond that.
Concerning the Gospels, we have a late anonymous narrative (Mark) filled with OT midrash that was anonymously redacted and expanded with even more midrash and legend. If this was the work of eyewitnesses, they surely would not have needed to cut and paste Mark and the OT as is evident the writers did.
The only mention of eyewitnesses I can think of is in 1Cor 15 that leaps out as a formulaic creedal interpolation. It reflects a later layer of mythmaking not even seen in the Gospels and Acts.
I know this review is not going to change your mind, but at least stop misrepresenting the position of those who are not convinced of the miraculous claims in Xtian writings.