I think Christianity has many worse examples of how it spread, countless examples by direct force, convert or die, especially for animists and polytheists. Islam was different in many cases, my understanding is that the 'small tax' you mention was asked to be paid, but of course if it wasn't there were consequences, and sometimes that was humiliation, at other times it was death. Islam is a very detailed and thorough religion that gives many answers which I think is the main reason why it was so successful and spread at an incredible rate (millions of square miles in a century or two at one point!), it gave enlightenment to many, but also conversion did at times come through conquest, even if choice was often given, or so we are to believe. Texts from the time are quite difficult to find. Muhammed was a philosophical military commander as well wasn't he? So the idea of warfare isn't uncommon in Islam, the region had been fighting each other long before he arrived after all, unfortunately it is something ingrained into early religion. The idea of Islam 'spread through the sword' seems fanciful and a deliberate insult on Islam to me, there was no real requirement for it. It was a natural progression from expansion.
