Yes the dominant culture was based on Christianity. So it acted through the legal system to protect itself and suppress others.
Note that a couple colonies/states only allowed Protestants to hold office. I guess Catholics aren't true Christians and can be oppressed by the Protestants.
What about Jews, Native Americans, African native religions, etc.? Native Americans were already here and enslaved Africans had no choice. Why would it be acceptable to force them to pay for & attend Christian services?
The First Amendment was a conscious effort to protect the citizens from having a religion imposed upon them by those using the power of the government. That is why official public school prayers are banned while voluntary prayer led by students on school grounds is permitted.