May Peace, Blessings and Mercy of Allah be on all of you!
The Intruder,you claimed that there are three 'groups' that are mistreated in Islam. This is pure misconception. No one is mistreated in Islam.
The Quran mentions equal rewards and punishments for both men and women.
I can give very many verses to refute your point. I'll mention a few here.
"For Muslim men and women for believing men and women for devout men and women for true men and women for men and women who are patient and constant for men and women who humble themselves for men and women who give in charity for men and women who fast (and deny themselves) for men and women who guard their chastity and for men and women who engage much in Allah's praise for them has Allah prepared forgiveness and great reward." (33:35)
Note that with every "men" there is the mention of "women".
"O ye who believe! ye are forbidden to inherit women against their will. Nor should ye treat them with harshness that ye may take away part of the dower ye have given them except where they have been guilty of open lewdness; on the contrary live with them on a footing of kindness and equity. If ye take a dislike to them it may be that ye dislike a thing and Allah brings about through it a great deal of good. " (4:19)
I don't think any explanation is needed. The highlited portion refutes your allegation.
Concerning slaves, theBeliever99 has quoted a beautiful verse. I hope you don't require anything more.
As for the unbelievers, Muslims are to respect them and their religion. But if the unbelievers are aggressive towards Muslims, it is obligatory for the Muslims to answer back. We Muslims are to invite the unbelievers to Islam, to teach them about Islam but never force them to believe in Islam.
You alleged a lot but did not mention a single Verse of the Quran or a single Sahih Hadith to support your claim. But you said that Muslims have done some atrocities. When you talk about Islam, refer to the Quran and the Sahih Hadith but when you talk about a few Muslims who are not following Islam correctly, it doesn't mean Islam is wrong. There are also some Christians who do the same. And there are also some Hindus who do the same. And there are also some Jews who do the same. "Some" people belonging to all religions are definitely wrong. But we can't say that the religion is wrong. I can give the example of the recent torture of prisoners in Iraq by the American soldiers themselves. But by this I cannot say that Christianity is wrong. To say that I would have to refer to the Bible.
I can even return the claim back to Christianity. Does Christianity treat women properly?
Leviticus 15:19-30 "And if a woman have an issue (her period/menses), [and] her issue in her flesh be blood, she shall be put apart seven days: and whosoever toucheth her shall be unclean until the even. And every thing that she lieth upon in her separation shall be unclean: every thing also that she sitteth upon shall be unclean. And whosoever toucheth her bed shall wash his clothes, and bathe [himself] in water, and be unclean until the even. And whosoever toucheth any thing that she sat upon shall wash his clothes, and bathe [himself] in water, and be unclean until the even. And if it [be] on [her] bed, or on any thing whereon she sitteth, when he toucheth it, he shall be unclean until the even. And if any man lie with her at all, and her flowers be upon him, he shall be unclean seven days; and all the bed whereon he lieth shall be unclean. And if a woman have an issue of her blood many days out of the time of her separation, or if it run beyond the time of her separation; all the days of the issue of her uncleanness shall be as the days of her separation: she [shall be] unclean. Every bed whereon she lieth all the days of her issue shall be unto her as the bed of her separation: and whatsoever she sitteth upon shall be unclean, as the uncleanness of her separation. And whosoever toucheth those things shall be unclean, and shall wash his clothes, and bathe [himself] in water, and be unclean until the even. But if she be cleansed of her issue, then she shall number to herself seven days, and after that she shall be clean. And on the eighth day she shall take unto her two turtles, or two young pigeons, and bring them unto the priest, to the door of the tabernacle of the congregation. And the priest shall offer the one [for] a sin offering, and the other [for] a burnt offering; and the priest shall make an atonement for her before the LORD for the issue of her uncleanness."
My main aim was to answer your post so I'll mention only this one verse.
Take care.