There are ~5 types of faith/belief in the Bible. Faith in God being real is consistently based on vast evidence and proof (see Luke 1:1-4 and Acts 1:1-4 and MANY other verses)
As Romans 2:12-16 and Acts 17:30 and other Bible verses say, God never condemns anyone for ignorance, or what they do not know. People are vindicated or condemned for refusing to follow truth that they HAVE been made aware of, but chose to reject. The reasons that Israel and other nations were condemned were different, since Israel had been given a lot more laws of freedom than other nations had.
If we didn't have free choice, we couldn't choose to sin. The reason God allows sin is precisely because He is NOT a dictator, and is allowing a demonstration of worldviews that want to compete with God's perfect government...so all in the universe and all people can see for themselves which way is better to live, God's or Satan's. This is brilliantly illustrated in the first ~20 minutes of this documentary.
There are averages for intelligence, but there are of course some very smart atheists/theists and some dumb ones. God doesn't work on averages in salvation, but with each individuals and the knowledge he/she has been exposed to.
if God could force us to love him, it would not really be love. Love is not love unless it is freely chosen:
“Power can do everything but the most important thing: it cannot control love…In a concentration camp, the guards posses almost unlimited power. By applying force, they can make you renounce your God, curse your family, work without pay…kill and then bury your closest friend or even your own mother. All this is within their power. Only one thing is not: they cannot force you to love them. This fact may help explain why God sometimes seems shy to use his power. He created us to love him, but his most impressive displays of miracle—the kind we may secretly long for—do nothing to foster that love. As Douglas John Hall has put it, ‘God’s problem is not that God is not able to do certain things. God’s problem is that God loves. Love complicates the life of God as it complicates every life.’”
In short, it all boils down to free will. If God made us unable to deny his existence, we would be unable to choose to love Him. Frequent, “impressive displays of miracle” would go further than merely doing “nothing to foster love.” Rather, they would render us much less able to choose to love God. It would take a fool indeed to reject a God whose existence is completely undeniable.