Is God ruthless or merciful?

Then He said to Abram: “Know certainly that your descendants will be strangers in a land that is not theirs, and will serve them, and they will afflict them four hundred years.  And also the nation whom they serve I will judge; afterward they shall come out with great possessions.  Now as for you, you shall go to your fathers in peace; you shall be buried at a good old age.  But in the fourth generation they shall return here, for the iniquity of the Amorites is not yet complete.” Genesis 15

So often when I'm discussing God with a nonbeliever and extolling His mercy and love and grace, I get the question 'What about the old testament where God commanded Israel to wipe out all the peoples living in the promised land?  What about all that murder and bloodshed? Would a loving God do such things?'

The answer is yes, God did. What I don't think we understand is the way God views sin. Because we sin every day, we don't understand that to God, sin is unbearable. It is depraved and horrid and in His holiness, He cannot tolerate it. All you have to do is look at all the rules and regulations surrounded the Jewish temple and worship to see that God takes sin and holiness very seriously. I mean the priests couldn't even enter the main part of the temple without going through a series of cleansings and sacrifices and sprinkling blood on themselves. Sin is contagious and it cannot come in contact with Holiness.  

God waited over 400 years, keeping the Israelites enslaved in Egypt while He desperately sought to get all the peoples living in the promised land to repent of their wicked ways and turn to him. 400 years!!  As he told Moses in the scripture above, Their iniquity was not yet complete. What does that mean? It means there would come a point when they would continually reject God over and over and would dive deeper and deeper into wickedness and at that point, God would give up on them. But before that He would keep reaching out, hoping they'd turn to Him. You see God didn't just love the Israelites. He loved and loves all peoples. I truly believe that if these Amorites and others would have turned to God, He would have allowed the Jews to intermingle with them and inhabit the land together. But they didn't. 

So why did God have them killed? Because sin is contagious. It pollutes the land. These people were sacrificing their babies to their gods. They were engaging in all sorts of sexual worship. They had to be removed or the Israelites would most certainly have been swayed to join in their sin.

But the fact that God gave them 400 years to change astounds me. I'm in all of His mercy! 
Yet, don't we as a nation sacrifice our unborn babies to the god of selfishness and convenience?  Aren't we also engaging in all kinds of sexual immorality? I wonder how long God is going to give us?