Christ's death was the end of sacrifice. None before were sufficient; none after were necessary. The Crucifiction was a once-for-all event; why then must Christ be sacrificed repeatedly thousands of times per day for thousands of years? and who are we to thrust His sacrifice upon Him again and again?
Wrong. Biblical sacrifice never ends with the mere death of the victim; read Leviticus if you don't believe me. The priest has to offer the sacrifice to God, and then (typically) he has to eat part of it, along with the person on whose behalf it is offered.
Hebrews 9 and 10 teaches quite clearly that Christ is now offering his blood in the heavenly Holy of Holies on our behalf as High Priest. That's an inseparable part of sacrifice.
why then must Christ be sacrificed repeatedly thousands of times per day for thousands of years?
I said nothing about Christ being "sacrificed repeatedly". Nothing in Catholic teaching claims to do that; it claims to make a single perpetual, heavenly sacrifice present to us on earth.
I missed the part where Jesus said, "Do this in memory of me... about five or six times, then stop doing this in memory of me..."
"The Crucifiction was a once-for-all event; why then must Christ be sacrificed repeatedly thousands of times per day for thousands of years?"
I recommend that you read the story of the Last Supper again. Jesus asked his followers to repeat this "in remembrance" of him.
The bread and wine of communion are a symbol of, or are transformed into, the body and blood of Jesus in the ceremony, depending on your doctrinal beliefs.
It is not a repetition of the sacrifice. It is a remembrance of the sacrifice. Some denominations celebrate communion frequently. Others do it just occasionally, but it has the same connotations in all denominations.
Transubstantiation is a Roman Catholic belief, based on the words of Jesus, who said that the bread and wine were the body and blood. Protestants think of them as symbolic. The difference is merely doctrinal, as far as I can see.
Christianity is, I believe, defined by the Nicene creed. The rest is interpretation.
It's Crucifixion (being fixed to a cross). Why do you put the word 'fiction' in there?
...why then must Christ be sacrificed repeatedly thousands of times per day for thousands of years?
Because He said so.
...and who are we to thrust His sacrifice upon Him again and again?
We are the ones whom He asked to do so.