At the same time, though, remember that Mark (whoever the person was, as we still don't know who the person actually was apart from the title) was writing for a community who was still suffering from the trauma of the First Revolt, when the Romans sacked and destroyed both Jerusalem and especially the Temple. At that point, the Sadducees vanish from the record because whatever authority the priests had as intermediaries between Palestinian Jews and the Roman Empire dissipated. Simultaneously, the Jesus movement (which proto-early Christianity was in those days, as a part of Judaism before the later split) was also trying to come to terms with the ramifications, since the destruction of Jerusalem also meant the original mother church lost all prestige and authority, leading to the rise of alternate power centers within the movement.
So, to whoever wrote Mark, the writer was trying to reassure his community that, yes, this is how people suffer and get persecuted because Jesus also suffered and was persecuted for his beliefs. Whether it's true or not, we actually do not know, and that is a question best left for faith rather than historical accuracy. What we do know is that Mark combined a bunch of oral traditions, a possible "sayings gospel" that must have existed (similar to the Gospel of Thomas in its structure and form, not necessarily in content), and delved into other sources, primarily the Tanakh in a pre-Masoretic form, to fill in gaps and provide linking narratives to tie it all together (let alone what later editors did to the Gospel through redaction and the addition of material, such as tacking on an additional ending that conforms with the ending in the other 3 Gospels when Mark's Gospel was designed to literally end with the empty tomb and people waiting, because that's the experience of persecution, as Jews, that Mark's community is familiar with).
It's because of that where we have to carefully approach the Gospel and ask ourselves - what did the writer mean by writing Jesus' trial as it is written? It is very likely blasphemy would not have been the actual charge used, since that much we know about Jesus' beliefs regarding that were pretty commonplace in 1st-century Palestine. Nor, for that matter, as a pious 1st century Palestinian Jew, would he have called himself a Messiah - though his disciples and followers surrounding him from the community may have believed that. Where it could come into problems would be the priests acting in place of Rome (and, in this case, to avoid Pilate's wrath) when it came to dealing with anyone who posed a potential challenge to the Empire. As a result, it would not have been dying "according to the Scriptures," but the Sadducees trying to translate something from Roman law into something that would fit the specific immediate context of early 1st-century Judea. That is what I mean about Jesus being seen as both seditious from a Roman point of view and the Sadducees being too overtly sensitive to ordinary criticism of their powers which everyone shared at that time.
So the writer of Mark is sending a dual message here. On one hand, suffering and being persecuted for their beliefs fits within the specific immediate post-First Revolt context of Mark's community. Maybe some of Mark's community were among the people who participated in the First Revolt and faced ridicule because of that. Maybe their views of Jesus were not quite in line with other early Jesus movement groups that have different views about Jesus. We don't know. What we do know is that by using the image of a suffering Jesus, and connecting it with prior narratives about people who suffer for the faith in the Tanakh that any Jew would be familiar with, including wholescale pilfering from the Book of Isaiah, the writer is comforting people in his community that everything will be OK because Jesus knows what the community is going through. On the other hand, tying it back to the OP, the writer is also using coded language - the blasphemy charge - to remind us of how aware people were about how challenges to the authority of Rome usually worked. In that case, excommunication and exile would seem the easier option. It would still be suffering, but it loses much of the immediate potency of connecting it with the First Revolt by granting Jesus a lighter punishment.
At the same time, though, we honestly do not know if Jesus actually said that, or if that was a later interpolation by redactors who were trying to soften Jesus' radical message by not offending potential Gentile converts who were loyal to Rome. Which would not be unusual in the ancient world to tamper with other people's writings in that manner.
