Whenever a Jew is killed, it is for the benefit of Islam. - Ahmad Sirhindi

Fighting the unbelievers and treating them harshly is one of the requirements of religion.

Islam and infidelity (kufr) contradict one another. To establish the one means eradicating the other, the coming together of these contradictories being impossible. Therefore, Allah has commanded his Prophet to wage war (jihad) against the infidels, and be harsh with them. The glory is Islam consists in the humiliation and degradation of infidels and infidelity. He who honours the infidels, insults Islam. Honouring (the infidels) does not mean that they are accorded dignity, and made to sit in high places. It means allowing them to be in our company, to sit with them, and talk to them. They should be kept away like dogs. If there is some worldly purpose or work which depends upon them, and cannot be served without their help, they may be contacted while keeping in mind all the time that they are not worthy of respect. The best course according to Islam is that they should not be contacted even for worldly purposes. Allah has proclaimed in his Holy Word (Quran) that they are his and his Prophet’s enemies. And mixing with these enemies of Allah and his Prophet or showing affection for them, is one of the greatest crimes…
…The abolition of jizyah in Hindustan is a result of friendship which (Hindus) have acquired with the rulers of this land… What right have the rulers to stop exacting jizyah? Allah himself has commanded imposition of jizyah for their (infidels’) humiliation and degradation. What is required is their disgrace, and the prestige and power of Muslims. The slaughter of non-Muslims means gain for Islam… To consult them (the kafirs) and then act according to their advice means honouring the enemies (of Islam), which is strictly forbidden…
The prayer (=goodwill) of these enemies of Islam is false and fruitless. It should never be called for because it can only add to their numbers. If the infidels pray, they will surely seek the intercession of their idols, which is taking things too far… A wise man has said that unless you become a maniac (diwanah) you cannot attain Islam. The state of this mania means going beyond considerations of profit and loss. Whatever one gains in the service of Islam should suffice…

The original aim of taking the jizya from [unbelievers] is for their degradation and this degradation [ought to be] to the extent that they cannot wear nice clothing for fear of the jizya ... and that they are always fearful and trembling ....