This is factually incorrect. God and Calvinism says all people are without excuse (Romans 1:20). (Aside: ignoring the 'age of accountability' issue).
Agreed, God and Calvinism say God made you "this way" Colossians 1:16-17. The bible and Calvinism also says God applies a remedy to those He chose (elected/predestined/appointed).
Regarding person born in 1200s who never heard of Christ you say:
So, your theory is that this fictitious guy is
saved by faith by instinctively knowing there is a moral law and trying to follow it.
Premise 1: John 3:18b the one who does not believe is judged already [that one has been convicted and sentenced],
because he has not believed and trusted in the name of the only begotten Son of God
Premise 2: A person born in 1200s dies having never heard of Christ
Conclusion: Your statement contracts scripture and therefore is false
again ...
Premise 1:
John 3:36 He who believes and trusts in the Son and accepts Him [as Savior] has eternal life [that is, already possesses it]; but he who does not believe the Son and chooses to reject Him, [disobeying Him and denying Him as Savior] will not see [eternal] life, but [instead] the wrath of God hangs over him continually.”
Premise 2: A person born in 1200s dies having never heard of Christ
Conclusion: Your statement contracts scripture and therefore is false
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Can they who have never heard the gospel, and so know not Jesus Christ, nor believe in him, be saved by their living according to the light of nature?
The Westminster Larger Catechism – Question 60
A60: They who, having never heard the gospel,[1] know not Jesus Christ,[2] and believe not in him, cannot be saved,[3] be they never so diligent to frame their lives according to the light of nature,[4] or the laws of that religion which they profess;[5] neither is there salvation in any other, but in Christ alone,[6] who is the Savior only of his body the church.[7]
1.
Romans 10:14, 2.
2 Thessalonians 1:8-9;
Ephesians 2:12;
John 1:11-12, 3.
John 8:24;
Mark 16:16,
4. 1 Corinthians 1:20-24, 5.
John 4:22;
Romans 9:31-32; Philippians 3:4-9, 6.
Acts 4:12, 7.
Ephesians 5:23
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https://www.gotquestions.org/inclusivism-exclusivism.html
Aside: There's a couple other people on this site that believe in "inclusivism" so your not alone. Thanks for responding. I think we know where each other stands.