Ironically you have refrained from using scripture to support your case...
I caught this late. Reformed Theology is SCRIPTURE, anything else is philosophy of men. How often have we seen a debate, we give scriptures "Lord why have you hardened our hearts so we fear you not", or inversely "The Lord opened the heart of Lydia so she could understand what the Apostles said", we quote that and what is the response? PHILOSOPHY, "Oh my God isn't like that", "Well that means that.......".
What liberals need to do is STOP JUDGING GOD BY THEIR OWN, FALLEN SENSIBILITIES. Doesn't scripture say "Lean NOT unto your own understanding, but trust in the Lord", but that's exactly what liberals do, each debate I see, whether here, online, or the over decade I've been debating liberals, they ALWAYS fall into that, "So if that is true, that makes God the author of sin", how many times have we heard that, or "Then men are robots", how about that one?.
It's clear when they say those things they are leaning unto their own understanding, if God says all things that come to pass are ordained by His hand, then all things that come to pass are ordained by His hand! We do not have the right to insert stupid ideas of our own, "Oh, so then God is the author of rape", and other blasphemy out of their ignorant lips. Many of these people are guilty of the severest of blasphemy, and they have no fear of it!
God's ways are not our ways, and if He states that He's decreed all that has come to pass, and has also stated that He is so pure that He can't even look at sin, it's OUR JOB to figure out how they reconcile, not just interject some ridiculous statement. But these, anymore it's truly hard to call them Christians, I've just done this so long, but THEY DON'T, they don't study the Westminster or London Baptist Confession, they don't study the greats, so they remain in ignorance.
If any man has the Holy Spirit in their hearts, which is what we were made for, that is we have thirst, there is water, we have hunger, there is food, we have a empty heart, there is God, ONLY HE can satisfy us, if God put His Spirit in Hitler, Hitler would repent, what about "I WILL TAKE OUT THEIR HEARTS OF STONE AND PUT IN A HEART OF FLESH" is so hard to understand? How is that a robot? When our hearts are filled with LOVE, JOY, PEACE, a sense of home, no man can resist it, so of course we believe, of course we stay. If I had my way I'd have left the faith along time ago, if I could lose salvation I would have, but God has said of our covenant "I will put the FEAR OF ME IN THEIR HEARTS so they won't leave me", again any learning disabilities here?
Oh yeah one last trick they try, when you nail them, they'll come back and try to mischaracterize a point you made or change the subject, "You misspelled xyz", or "You sound judgmental", or "You can't say X", but NEVER can they out debate us, for they are debating God's word. Every scholarly debate online, I mean the best, Doctor so and so versus Doctor so and so, the liberal ALWAYS falls into philosophy.
Doesn't matter whether it's Systematic Theology or Biblical Theology, Liberal Arminians ALWAYS come up short, their only way to attack is what this guy is trying "well your philosophical", he can state that, BUT HE CAN'T DEBATE YOU ON SCRIPTURE. Don't let it bother you, it's just another diversion.