I've known Calvinist my entire life and have debated their doctrine for decades. You are just simply wrong.
Calvinist universally quote John 3:16 and believe that Jesus died for the whole world. They have a different (wrong) understanding of what Jesus meant by "whole world" but that does not equate to them denying that Jesus' death was propitiatory. They absolutely do believe that Jesus died for sin. There are LOTS and LOTS of things that Calvinists get wrong but whether Jesus' death had to do with paying for sin is not one of them. They deny that Jesus died for all sin but one of their major tenets is specifically about the fact that Jesus' death atoned for the sin of the elect. To deny that would just be aggressively stupid.
Jesus' death did, however, have to do with with more than just paying for sin. That is to say that His death accomplished more than just the satisfaction of justice. That was the key issue but there was more accomplished at Calvary than just that. There are all sorts of very deep spiritual truths that are all included in what is rightly called "the gospel" and, just to give one example, if some Christian pastor wants to give a sermon or a Christian lay person wants to have a discussion with his neighbor about how we are identified in Christ and that allowing Christ to live His life through us is the key to overcoming sin in our lives, then there is no requirement to also discuss the specific issue of Christ dying for sin at that moment. The gospel is a rather complex set of doctrines that are all intertwined and connected together. To discuss one aspect of the gospel does not imply the denial of other aspects of it, which seems to be what you are implying.
In short, you're debating Limited Atonement, which is a doctrine that I've come to believe that no one can fully understand AND believe without their mind being broken. There are so many passages that just flatly contradict it, many of which you've quoted in this thread, that anyone who accepts it is in one of three categories; they are either deceived, delusional or deceptive. Those in the third may or may not also be in either of the first two but in any case, the doctrine is foolishness and you are right to appose it. I would simply tell you to appose it and not some other convoluted thing that no one accepts as true. There is no Christian who denies that Jesus died for sin. Such a person just doesn't exist and debating people as though they are one of these people only make you look like the lunatic.
There is one other possibility that just occurred to me while editing this post. It could be that you are advocating Universalism which is one of the very few doctrines that are more intellectually unhinged than Calvinism. I'm really hoping that this isn't the case.
Clete