According to Acts 5, people who are fighting against God are people who,
by trying to attack religious freedom, find themselves prohibiting truth reaching others.
Some disciples had been arrested and put into prison. Sanhedrin priests were prohibiting them to preach.
Gamaliel then called those priests to stop pestering the disciples, regardless of whether their doctrine was man-made or God-made. Gamaliel called for respect to religious freedom.
Let's read
“Men of Israel, take heed to yourselves what you intend to do concerning these men. 36 For in previous days Theudas rose up, boasting to be somebody, to whom a number of about four hundred men joined themselves. He was killed, and all who obeyed him were dispersed and came to nothing. After Theudas, Judas the Galilean rose up in the days of the census and drew away many people after him. This man also perished, and all who obeyed him were scattered. Now I tell you, keep away from these men and leave them alone, because if this intention or this activity is of men, it will come to nothing. But if it is of God, you will not be able to overthrow them, lest perhaps you be found even fighting against God.”
Therefore, unless people are making a call to do evil, or prohibiting religious freedom, people presenting their doctrinal arguments should
not be considered as
"fighting against God" just because their arguments are wrong. If we are not careful with our language, we are planting the seed of violence towards "spiritual enemies" of our own invention.