First, the whole rubbish about sinning against the holy spirit is to prevent anyone that finds out what it is from blabbing the secret to everyone else. The "sin against the holy spirit" is finding out that the whole platform of Christianity is rubbish. And, if they were allowed to spread the truth about Pauline and Augustine Christianity to everyone else, they would find that it doesn't match Jesus' own teachings. Let that happen, and the churches and Kingdumb Hells would implode. So they need to use "sin against the holy spirit" to limit the damage people can do by exposing their religion as a scam.
And, of course, it is used to generate fear. Tyrants seem to love Christianity as a platform, and they use that "sin against the holy spirit" to defend the status quo. They also use it to get people to do more--missionary work, monastery style work, and selling out. They also prevent people from enjoying their lives--if you persistently do something as wimpy as homosexuality or gambling, that you are not able to quit doing it could be "sin against the holy spirit". As they are afraid of those who figure out what their "sin against the holy spirit" rubbish is (a defense to prop up their scam), anyone that does these made-up sins and cannot give them up is afraid that they may have "sinned against the holy spirit". Same thing about people that don't see what's wrong with having a little fun and are not sorry enough that they are gay or that they drink or gamble.
And, questioning the religion is one prime example of using the "sin against the holy spirit" rubbish to maintain the status quo. Don't question the pope or the Filthful and Disgraceful Slavebugger. Just believe what they say and do accordingly. Of course, the result is that the religion, already on a rubbish platform, is going to be even worse rubbish.
