While Islam seems to teach that all Muslims will go to heaven, and peace loving, kin - even charitable - non Muslims will not, I struggle to grasp the idea. I, for example, find it unthinkable that a man such as bin Laden who killed thousands of people, would be with me in heaven. I don't think Allah's got this one right. Why should mere belief dictate fate?
In the name of God, the Most Gracious, the Most Merciful
Your question: Why should all Muslims go to Heaven?
Because, it is the way of life, I mean when God created Adam He Created also Islam and He decided that the one who died as a Muslim will go to Heaven even if he/she is is Punished, because it is something that God Almighty Says:
”For those who believe and do righteous deeds are Gardens as hospitable homes for their (good) deeds.”
"This day have I perfected your religion for you, completed My favour upon you, and have chosen for you Islam as your religion". (Soorah Al-Maa'idah 5:3)
”If anyone desires a religion other than Islam (submission to God never will It be accepted of Him" (Soorah Aal'imraan 3:85)
”For We assuredly sent amongst every people a prophet,(with the command) worship meand avoid false gods " (Soorsh Al-Nahl 16:36)
Thus, the final Prophet of Islam is reported to have said, "Any one who says: There is no god but God and dies holding that (belief) will enter paradise".(Reported by Abu Dharr and collected by Al-Bukhaaree and Muslim).
And by submitting to God will make you earn His mercy and grace and will make you enter Heaven because it is the only true religion.
Your statement: non Muslims will not go to Heaven is wrong.
That is because being Muslim is not a guarantee of heaven, and being non-Muslim is not a guarantee of hell. Humans are not allowed to judge whether any person is going to heaven or not.
What we can say is that Islam is the straightest path to Heaven, and those who try to follow the true message of God are the most likely to achieve salvation. However, I cannot guarantee to you that I or any other living person is going to heaven or hell - all we can do is pray for God to guide us, then follow that guidance and hope for His mercy.
God is the only Being capable of knowing every thought, feeling and action of any person. Only God knows our sincerity, our intentions, and every past experience or inner emotion that influenced our beliefs and decisions. God will judge non-Muslims based on the opportunities and knowledge they were given. God does not oppress anyone and He is the most Just. God Says:
”...And We never punish until We have sent a Messenger (to give warning)”
And remember that God is the Most Just and Most Merciful and if anyone who died without hearing the message of Islam in correct form or nerved heard nothing of Islam nor about prophet Muhammad will not be Punished by God on the Day of Resurrection but that disbeliever will be tested by God on the Great Day, if his disbeliever obeys Him will enter Heaven if he does the opposite will enter Hell, you know what I mean? Oh and, even if a Muslim is punished by God on the Day of Judgment then this Muslim will stay in Hell for a short period of time and then God will Take him out and put him in Heaven and that is mentioned in Quran.
First of all, about disbelievers who are kind and charitable people, why should Allah forgive someone who has never sincerely asked for forgiveness? Yes, they were good to other people for their own reasons, and Allah will reward them with whatever they did good deeds for.
But, the reason a muslim's good deeds are better is because they are done for the sake of Allah, and so he will be rewarded with the happiness of Allah. Even a muslim's good deeds if done for the wrong reasons are of no use.
Regarding Muslims who have done terrible things, murder is indeed a terrible sin:
Because of that, We decreed upon the Children of Israel that whoever kills a soul unless for a soul or for corruption [done] in the land - it is as if he had slain mankind entirely. And whoever saves one - it is as if he had saved mankind entirely. And our messengers had certainly come to them with clear proofs. Then indeed many of them, [even] after that, throughout the land, were transgressors. (5:32)
And Allah will punish those who are guilty of sins justly and fairly on the Day of Judgement, even muslims.
Man will be informed that Day of what he sent ahead and kept back. Rather, man, against himself, will be a witness, Even if he presents his excuses. (75:13-15)
Everything will be accounted for properly.
Now, about the fact that believers are eventually forgiven:
There shall come out of Hell-fire he who has said: There is no god but Allah and who has in his heart goodness weighing a barley-corn; then there shall come out of Hell-fire he who has said: There is no god but Allah and who has in his heart goodness weighing a grain of wheat; then there shall come out of Hell-fire he who has said: There is no god but Allah and who has in his heart goodness weighing an atom.
Our actions are not enough to repay Allah for all he has done for us. Only through his forgiveness does anyone enter Jannah. And as the above shows he is willing to grant his forgiveness (he is Most Merciful). All you have to do is ask and also have an atom of goodness in you. Acknowledging his existence and oneness (saying La ilaha illa allah) is the least that can be done.
In conclusion, everyone will be punished for their sins, but genuine muslims will be forgiven in the end because they asked to be forgiven, and they have an ounce of good in them. No persons actions make him deserve Heaven. It is only through Allah's forgiveness that one enters it. Forget about anyone specific like Osama bin Laden. You or I don't have any idea of what was in his heart, and we can't say if he will or will not enter Heaven.
And Allah knows best.
Perhaps an analogy will help you understand: Killing 100 ants is not as bad as slapping the Queen. Think about why this is. -- It has everything to do with STATUS. You cannot compare an ant to a human life; likewise, you cannot compare a human to God (the Most Supreme).
Disrespecting Allah (ﷻ) is the worst thing you can do.
By disbelieving/disobeying Allah, you've demonstrated ingratitude of the highest magnitude and shown that you are not worthy of Paradise. Point blank. Your other "charitable deeds" don't make up for this (surely you follow the logic in this; eg, if you are a rapist, just because you do some other thing that classifies as "good" doesn't mean you are good). Only one thing makes up for this, and that is sincere repentance and belief/obedience of your Maker.
Every sinful Muslim at least believes and respects His Lord; that is the best deed. (And they don't go and make statements like "I don't think Allah's got this one right" demonstrating ingratitude and an arrogant belief that they know better than their Lord, which is disbelief).