I've often wondered why a loving and gracious God would punish people so serverly for even the tiniest sin(s). What if they lived a decent life?
You seem to be bothered by the thought that all sinners are worthy of hell, apart from Christ. You speak of "the tiniest of sins," which I find quite interesting. The Bible says that sin is lawlessness (1 John 3:4; see also Romans 5:13), which doesn't sound so tiny. Sin is breaking God's law (Romans 3:19-20). Even the heathen are guilty before God because they reject what God has revealed about Himself in nature (Romans 1:18ff.).
You ask about a non-believer who lives a semi-decent life. The fact is that the scribes and Pharisees lived very decent lives, but their "righteousness" was self-righteousness, a very special offense to God - trying to be good on your own. This is why Jesus was gracious to sinners (like the woman in John 8:1ff.), but so hard on the self-righteous scribes and Pharisees, whom He frequently called hypocrites (see Matthew 23).
Your struggle with "tiny sins" can only be resolved by further consideration of the holiness of God and the fallenness of men.
You may wish to look at these lessons:
By the way, if you stop and think about it, eating a piece of forbidden fruit didn't seem like such a serious sin either, but it plunged the whole human race into sin and death.
Related Topics: Soteriology (Salvation)