Are we? Firstly, there is nothing in the Bible to indicate that God has a body. Secondly, look at what Jesus says:
Mat 22:37 And he said to him, “You shall love the Lord your God with all your
heart and with all your
soul and with all your
mind. (ESV)
So, according to your reasoning, we are actually body, heart, soul, spirit, and mind. To claim that "we are a trinity," by limiting it to three aspects of humanity, is completely subjective.
Of course "there is no need to divide us into three separate persons," as we know that we are only one person.
What ammunition would we be giving them?
Three problems. First, you're ignoring one of the difficult points for your position that I have given several times in this thread. There is not a single verse in the entire Bible that clearly or explicitly states that God is an absolute unity, that is, only one person. Not one. Second, we are not tripartite persons.
Third, God is certainly not a tripartite person. If he were, then it logically follows that he could not have been God prior to the incarnation
and the existence of the Holy Spirit as separate from the Father. Tripartite means that the one is composed of three, that is, it takes three separate parts to make the whole. That means God is divisible. To use that language of God is incredibly problematic for your position, and has nothing to do with the Trinity.
Who is a laughing stock and why?
A common but erroneous understanding. Constantine had little, if anything, to do with the conclusion of the Council of Niacea. Christian theologians and leaders
later developed, or rather discovered, the doctrine of the Trinity. Constantine merely brought bishops together to try and get them to come to a consensus about who Christ was and is, largely due to the division Arius was causing. Division in the Church meant a divided kingdom. He oversaw the proceedings and may have participated in discussions, but apparently didn't cast a vote.
It was a Christological debate, not a Trinitarian one. Do you disagree with the Nicene Creed?
https://overviewbible.com/council-of-nicaea/
https://www.britannica.com/event/First-Council-of-Nicaea-325