"My little children, I am writing these things to you so that you may not sin. But if anyone does sin, we have an advocate with the Father, Jesus Christ the righteous." 1 John 2:1
So does everyone have an advocate with the Father -- Jesus Christ the righteous? Because if Christ Jesus is advocating the same for Christian and non-Christian alike, and to Christ Jesus has been committed the Judgment, then 1 John 2:2 proves too much. Whereas the rest of Scripture states that some people shall not be saved by Christ, this passage would indeed deduce to universal salvation.
That's largely why Calvinists reject this interpretation of 1 John 2:1: it oversells the point.
A point much more in line with Scripture is that Christ is the one appointed for turning aside God's wrath: so that if He does so, then the wrath is indeed turned aside. But if He doesn't -- well, I hope they're wearing asbestos underpants. That's the position of Calvinists for this passage: that Jesus is the sole one with this role, in redemption of the Universe (that is, the "kosmos"). But He's not actually propitiating for each and every person -- nothing's really stated about individual people in this verse.
I find this specific verse vacuous on universality, and here's why.
The verse doesn't have two conjoined groups it saves. It's not "all men and those who believe" -- it's "all men especially (or, particularly) believing". That one group of believers is not even in question.
Plus, as it's understood in this way, again, it proves too much. If God saves all men, and then particularly saves believers -- well, what's the result? God saves all men. But no, it's not two groups -- it's "all men particularly believers".
We do this all the time -- particularly now. "all" isn't pervasive, it's a modifier of the nouns in the sentence; "particularly" is an additional modifier to items in the sentence, including apparently the phrase "all men". "all ... particularly" should therefore be understood in its common usage of the day: not "each and every one", as that's represented in Greek in another way when the writer/speaker wants to assure us of that situation.