You've given so many examples the forum can't handle adequate answers. If you want real answers, and not soundbites, we can't deal with so many misunderstandings all at once. I'll answer briefly, but you have to understand that the answers aren't complete. There isn't room for complete answers.
> The same God that says "thou shalt not kill" committed acts of excessive violence against the Egyptians, the Caananites, the Midianites, and many other groups -- millions of people were murdered at God's command during the exodus, the conquest of Caanan, and its aftermath.
You have a serious misunderstanding of these events. They have been discussed many times on this forum. I could refer you back to those discussions, or we can have them again on a separate forum (no room here for everything). Suffice it to say, God did not commit excessive acts of violence against these people groups, as you have falsely accused.
- His acts of judgment against the Egyptians were aimed at their perverse and deceitful religious system. All of the plagues were to break down their religious lies, even the final one. Much longer explanation is warranted.
- The alleged "genocide" against the Canaanites and Midianites is a misunderstanding. No population groups were wiped out, nor were children being slaughtered. It was warfare rhetoric not actuality, for one, and second, the intent was to do away with the Canaanites' identity as a people group, not to kill them off. Much longer explanation is warranted.
> The same God that says "thou shalt not steal" led the Israelites, his chosen people, in a bloody conquest to steal the land of other nations away from them.
The ONLY land that Israel was to take was Canaan, which was given to the Israelites and promised to them. According to the Bible, the Canaanites were the squatters. The Israelites went to war to recover what was theirs. Other than Canaan, the Israelites were never authorized to engage in offensive battle, and there was never any effort to expand their country into other lands.
> The same God of whom the psalmist David later wrote, "His mercy endureth forever" instructed the children of Israel to "show no mercy" to the inhabitants of the Promised Land. He commanded them to kill everything that breathes, including women, children, infants, and animals.
Same conversation as the false "genocide" accusation. The "kill 'em all" was warfare rhetoric, not meant to be taken literally. Secondly, the term often translated as "kill 'em all" is herem, which has been found to more accurately mean, "remove from human use" rather than "kill 'em all." Many "herem" items had nothing to do with death and destruction. The Israelites only destroyed 3 cities in the Conquest: Jericho, Ai, and Hazor. Much longer explanation is warranted.
> he same God who says we should forgive others will refuse to forgive others at the Great Judgment.
Forgiveness is conditioned by repentance. You have your whole life to repent. You can repent even now. Don't wait another day. If you refuse, don't blame God for your decision. Any judge worth his salt knows how to vindicate the innocent and pronounce verdict on the unrepentant. If a judge forgave all crime, he wouldn't be much of a judge, and crime would become the norm. That's no way to run a kingdom.
> God strikes down the firstborn of Egypt after God hardened pharaoh's heart so that pharaoh would refuse to release Israel from Egyptian bondage.
- Pharaoh hardened his own heart. A much longer explanation is warranted.
- The Egyptians had slaughtered the Israelite children. Retributional justice is fair.
- God's actions against the sons of the people is a strike against their religious lies. A much longer conversation is warranted.
> King David committed adultery ... So God punished David by killing his newborn son (2 Sam. 12).
- In the ancient Near East, including Israelite culture, there was no distinction between natural and supernatural. Their perception was that God or the gods were involved in every detail of life. Thus anything that happened was considered to be an act of God. It's not surprise they word it this way. Any death was "God killed him." Any life was "God spared him." The Lord closed wombs; the Lord opened wombs. Everything was perceived as an act of God. It is very active language that shouldn't be taken in a modern sense. At the same time, the author's point is that David is being judged by God for his sin. If you look at the whole story of David, you'll discover that David loses 4 children as a result of what he did. One son murders another. One son is executed by David's general. This son dies of some kind of disease.
- In our modern way of thinking (whether it's more accurate or not is impossible to say), we would not word it this way or understand it this way. We would say the child died a natural death, and that David was cut to the heart with grief, and that was his judgment. But since they saw no distinction between natural and supernatural, they expressed it differently. That's not to claim that the child would have lived anyway. The child may have been born very sickly and was so unhealthy he was going to die. That's how we would say it. The way they said that was "The Lord struck the child and he became ill."
- It was perceived, along with the eventual deaths (by completely different and unrelated means) of 3 more of David's sons, as David's punishment for his adultery with Bathsheba. That's what makes it justice. The text is concerned to show us that David is paying for his sin with his family (his offspring, and therefore "eye for eye" for adultery) going to ruin and his heart being filled with unquenchable grief.
> David took a census ... God killed 70,000 people with pestilence.
God knew there was compromise, idolatry, and ungodliness in the nation, and inciting David to take a census was a mechanism to bring out the truth of that, and how corrupt the people were. Given that the case was established, judgment was pronounced and the punishment executed. A much longer discussion is warranted.
It’s just like Jesus saying to the woman at the well, “Go get your husband,” knowing full well she didn’t have one. The suggestion of the action reveals the truth of the sin.
> God said numerous times that he visits the iniquity of the fathers upon the children even to the third and fourth generation (Ex. 20:5, Ex. 34:7, Num. 14:18, Deut. 5:9).
If you study the text, you'll see that this is more descriptive than prescriptive. Sons tend to be like their fathers, and fathers train their sons to be like them. Sin in the family can last for generations. God isn't punishing people for what was not their infraction. A much longer discussion is warranted.
> The nature of the God described in the Bible is both contradictory and oftentimes, ruthless.
Your misunderstandings are deep and severe. A much longer discussion is warranted.
> So in conclusion, even if there were evidence that the God of the Bible exists, why would anyone willingly worship him?
Because you have misunderstood just about everything about Him. We can talk more, as you wish.