One objection atheists bring against the love and justice of God is that really, God is punishing us for breaking laws He made up. He could have made a set of laws we actually want to keep, or He could have just made no laws at all, yet He chose to make a set of laws He knew we'd break, seemingly just so He could punish us for breaking them. Therefore, He is either unloving, since apparently He likes watching us suffer, or He is unjust, since He could have saved us, but chose to make us suffer.
Now, the first problem with this is that it contradicts another objection atheists like to raise against God: the Euthyphro dilemma. The Euthythro dilemma is simply this: Is good good because God says so, or does God say so because it is good. If the former, then God can rightly be called arbitrary. He can call violent gang rape good and it becomes good, He can say charity is bad and it becomes bad. "Good" is then a meaningless term, because it becomes subject to the whims of a capricious deity. If, by contrast, God merely says good is good because it actually is good, then there is a higher standard than God, and He Himself should be subject to it.
Of course, the correct answer is that God is not arbitrary. Both sides of the dilemma are compatible. God calls good good because it is good, and it is good because God calls it good. Why? Because He is the sole and sovereign Creator. Good is when a thing works as God intended it to work, and not good when it does not. The bottom line here is that God is not arbitrary in how He makes up His rules. He could not have given us different rules unless He also had different intentions when He did so.
What's funny, though, is that God is the only one to whom atheists would apply such silly logic. Tell me, you parents, do you give your children rules? Of course you do! Do you punish them for breaking those rules? I would hope so. Yet, I would assume most of these rules are not arbitrary, and the punishment fits the crime. You bet I'll give my daughter a jolly good crack on the butt if she runs into the road. I'd rather she suffer the pain of my hand than go to her grave before me. If my son should strike another child, he likewise will receive strikes, because I will not be raising a violent man, but a gentle one. A good mantra for any child to learn: "Control yourself, or you will be controlled." A good parent gives rules because for the short time you have raising your children, they depend on you to teach them how to survive, and live long, fruitful lives. If you don't set rules, or punish them for breaking them, that's not loving, you're a bad parent, because they might not even survive childhood, much less thrive after.
And in fact, even if they do survive childhood, there is another entity that will punish them if they should break their own rules: The government. The government makes rules all must abide by, and they will punish you for breaking them. Yet, no one raises this objection against the government. It is only against God. We somehow recognise that a parent, or the government, are just for enforcing their own rules, yet apparently, we do not recognise that God is likewise just for doing the same?
What's more is that even we set seemingly arbitrary rules. How long does my kid get to spend on the internet? What time do they have to go to bed? Am I going to try to get them into a specific extra-curricular activity? These vary from parent to parent, yet no one questions them. Similarly, the government sets seemingly arbitrary rules (and let's be honest, the government is significantly more corrupt than it ought to be, which is why I defaulted to using parents as the primary example) that no one questions. Which side of the road do we drive on? What denominations should our currency be divided into (and should each denomination be a coin, or a note)? These are rules which can vary from country to country, yet we pretty much leave these rules to each country.
As previously established, God's purpose for His rules is not arbitrary. Rather, He designed us and our universe for a specific purpose. Furthermore, He is significantly more qualified than any parent or any government will ever be to not only make these rules, but justly enforce the punishment for breaking them. Why? Because He is both sovereign and omniscient. He knows the end result of every possible variable; variables we aren't even smart enough to consider. "What would happen if I made every man an inch taller? What would happen if I invented an 8th color? What would happen if I wrote my Scriptures in the clouds instead of a book?" God knows the answer to every one of these questions. But He chose to do it the way He did it, because He knew the end result would be the one He intended.
As for enjoying watching us suffer, just look at the lengths He went to to make sure we didn't have to. Even though we broke God's laws, and thus deserve punishment, Jesus Himself took that punishment on our behalf, ensuring that if we just repent, confess Him as Lord and believe, we would not only be forgiven for our sins, but rewarded for His justice! If we freely reject that gift and choose to instead receive our punishment ourselves, that's not because God wanted to punish us, it's because we wanted the things that earn us that punishment more than we wanted what He wants for us. There is truly no end to the atheist's insanity in trying to blame God for our sins. Repent, and be saved!