Critics of Muhammad today suggest he was in the same league as Hitler, Mao, Stalin, Nero or Attila the Hun in terms of how he forced his people backward and oppressed them, but it seems it can also be argued his actions were more good that bad when the situation of Arabs before and after him is analyzed.
Except for the massacre of Jews, I don’t think one can necessarily equate Muhammad bin Abdillah with the likes of Hitler, Mao, Stalin, Nero, or Attila the Hun. Muhammad’s reach was very local – except for missionary assignments, Muslims of Muhammad’s time stayed within the Arabian peninsula. Furthermore, while the sword of Islam brought many tribes into the Islamic polity, more tribes were integrated into the Islamic state through diplomatic means, mainly through marriage. While it is true that Muhammad had many, many wives, most of these marriages were for political, diplomatic purposes.
This is evidenced by what happened as soon as he died – many tribes that were allied with the Islamic state defected. They saw their inclusion in the Islamic state as a political not religious arrangement. They saw Muhammad not so much as the prophet of God but rather as super-chief of all tribes. Hence the Wars of Apostates under Abu Bakr, Muhammad’s successor as political leader: he fought these defecting tribes to keep them in the Islamic polity, enforcing the religious (rather than simply political) nature of the Islamic state. (Muslims often characterize the tribes as having converted to Islam where they really simply joined a political union.)
Now, did Muhammad create a better environment? If we believe what the Muslims (obviously biased) have written, then yes. But if we want to be absolutely sure, we need a better idea what pagan Arabia was really like (rather than what it was alleged to be). Very few descriptions exist of pagan Arabia, so we can’t really say.
That said, I do not think it can be said that Muhammad initiated a regress of the Arabic people. Critics may not want to swallow this bitter pill, but Muhammad (and Muslims) did a lot to advance the Arab peoples. In a short span of time, desert nomads had conquered ancient kingdoms and ruled vast swathes of land. One can hardly call this forcing the Arabs backwards. Were it not for Muhammad, the Arabs would be nobody today. Islam put the Arabs on the world stage.