Having been on the receiving end of some of this Calvinism hatred; at least in my particular case, it basically had to do with the other person's concept of God.
He sees the Calvinist understanding of "Limited Atonement" to be a very cruel and mean and vindictive God, who picks and chooses who goes to hell and who doesn't.
It really doesn't matter if a Calvinist tries to correct this misinformation, because their mind is already made up.
I got the idea that if they found out Calvinists were correct concerning "Limited Atonement"; they would no longer want to serve a God like this.

I can sort of understand this line of thinking, mainly because although I was never closed to "Limited Atonement", never the less I lost a lot of sleep over trying to understand what I was seeing Scripture teach concerning this matter.
After a while, I embraced this doctrine, but didn't understand it. It was about 2 years as a Calvinist that I realized I had been thinking this issue through the lens of my own eyes, rather than through the lens of my sovereign God.
I can honestly say that this new way of thinking was very freeing and it brought new prospective in such areas as evangelism and every day life.
God is sovereign in every area of life. BigThumbUp
This isn’t to say that “Limited Atonement” is the only area that causes “Calvinist hatred”, but I have found that it probably causes the most hatred.

Tom