Actually, there's many Christians who do that today out of ignorance but they might be guilty. However, I knew about Jesus Christ and at age 14, I foolishly believed what the Pharisees said when they called the Holy Spirit a demon. I wish that I never heard about this sin but I messed up more than 99.9% of the world's population. I don't know why I couldn't have been a normal kid and a normal person. What you described can actually happen today as well and it happens many many times.
Sorry but I think you misunderstand me.
This was not a sudden change of character from immoral to moral, nor a misunderstanding of scripture, or a possible healing that could be attributed to anyone other than God. This was not one or two signs like Marys face in a bit of toast or weeping statues seen by a select few.... This was not something the blasphemers could have misunderstood, rather they KNEW it was God, for according to their own teachings, only God could do the works Christ did.
The Jews seek a sign the scriptures say, and He gave them what the scriptures told them God would give them.
These days there are so many false teachers and fake healers and name it and claim it fraudsters that anyone could be forgiven for not knowing if a healing is real or fake etc. We see a lot on tv, in showmanship style and if there are real miracles they are lost amidst the performances that rake in the cash from desperate souls.
The miracles Jesus did, MANY MANY MORE than we read about by all accounts too, were such things that a whole community witnessed and testified to one another that it was real. People they all knew, blind from birth being made to see. People they knew paralysed for years suddenly walking about giving glory to God.
This power was indisputably God. What we Christians experience of the acts and power of God, cannot be compared with the which He himself displayed as evidence and testimony HE was the walking, living, flesh covered, breathing Messiah on earth. What we can testify to en mass today is generally not what the Jews experienced when Christ walked the earth. At best we can thank God for a few healings are and there, and share our testimony of changed lives. Glorious, but no comparison to the undeniable evidence the Jews were facing at that time.
The pharasees KNEW it was God, there was no mistake, no confusion, no delusion, but declared it was Satan because they did not want people to believe in Jesus. This is what I am saying is SO RARE, only Jesus did the amount, type and concentration of miracles He did whilst on earth. He had to fulfil the prophecies to the Jews.
This is why I doubt many Christians today can commit the same offence.