Well, yes and no. The origins of Christian veneration of saints began with graveside vigils of particularly holy people (literally, ‘saints’) on the anniversary of their martyrdom. [It is quite common to remember one’s dearly departed on the anniversary of their death.] This has nothing to do with polytheism, ancestor worship, or pagan rituals. It’s a human thing done by Christians.
Certainly, Pagan influences shaped the development of the practice of a more ritualized remembrance of the martyrs and other famous ‘saints.’ As has been pointed out already, a paricular tribe may miss their harvest god and the accompanying festivals of that god when they converted to Christianity. The solution was to promote a farmer-saint as the model farmer and to hold the festival in his honor. Pop historians (namely, neo-Pagans with an axe to grind) will then wrongly claim that Saint Farmer was actually Harvest God, borrowed by the Christians.
The beginning of the ten commandments will certainly back you up on the monotheism. I think you’ll be hard pressed, however, to come up with explicit New Testament citations that each member of the trinity is to be worshipped. (You won’t even find ‘trinity,’ ‘states,’ or ‘persons (of the trinity)’ in the NT.)
Ummm, not wanting to sound harsh, but… you actually believe as factual anything a fundamentalist says about their enemy without doing some fact checking on your own?
D&D is not (necesarily) a Satanic ritual. Bill Clinton is (probably) not the anti-Christ. The world will (most likely) not end next year. And Catholics don’t worship saints.
Catholics ‘talk’ to the saints, like most people do to departed loved ones. And this communication with the saints is called ‘prayer.’ Not all prayer is ‘worship.’ It is official RCC teaching that only God is worshipped, Saints may be venerated, and you can ‘talk to’ any non-living human, whether they be the dead, angels, or God. It is this broad definition of ‘prayer’ that causes Protestants to think that Catholics are worshipping saints.
And yes, this ‘prayer’ to the saints has been abused by many Catholics as a magic formula to gain spiritual favors. It was a medieval construct to think that the saints, who are mulling around the court room of God the King, have access to the King’s ear. And just like they’d butter up and seek favors from local officials, they thought they could do the same with the saints. This is not official RCC teaching. But it is a popular custom which is difficult to stamp out – like belief in horroscopes.