It says that YOU.... may know... that YOU have... I actually originally italicized the you’s in that Scripture because I figured you'd say that, but the fact still stands John didn’t have any issue with people knowing they HAD eternal life. John didn’t even say you’re going to have, John past tenses it pointing to the moment they believed. He’s so cool and eager for them to know they have eternal life. He writes them a letter about it!
”I write these things to you so that YOU (insert readers name here) may know (confidently understand) you HAVE (currently possess) eternal life.”
You are making the classic OSAS mistake. You are defending a concept that is not in question.
The issue of whether or not Christians are granted salvation is
not in debate, The issue of whether or not Christians can feel assured of salvation is also
not up for debate. The weak and dangerous link in unquestionable assurance is simply the assumption that we cannot be wrong about our
quality of belief.
John's letter was read to the church as a whole, to assume that everyone hearing the message was being told that their salvation was guaranteed would be foolish. John was making a true but general statement that the Christians were guaranteed salvation
not that all who claimed to be Christian were guaranteed salvation.
Salvation is assured to Christians
not to those who sincerely believe they are Christians.
Mormons misuse the same verses as you, they too believe the "you" applies to them individually. Where the potential for false assurance exist, true assurance cannot.