Board Thread:Questions and Answers/@comment-28067574-20190904162421/@comment-26907577-20190911112326

That seems unlikely. My money is on Toriel not making that proposal until the ending.

"A monster with a human SOUL... a horrible being with unfathomable power."

Asgore would know that he could easily take six more SOULs and go back to shatter the barrier. The only explanation is that it never crossed his mind, at least not before he declared war and started procrastinating.