It may be an emotional and philosophical argument, but its not a legal one.  A jury of 12 people, when the law and the facts were explained, voted that Mr. Rittenhouse had the right to be there, had the right to be armed, and had the right to not be attacked, and when attacked, had the right to defend himself with lethal force. 

You may feel he should not have been there, but the law allowed him to be present and armed.  Many older and presumably wiser/more experienced individuals did not find themselves in Mr. Rittenhouse's situation, and presumably were either taken more seriously by protesters or had the ability to deescalate more serious provocations that Mr. Rittenhouse did not.

Unfortunately, a mentally unwell man attacked Mr. Rittenhouse and the rest is history.  If Mr. Rosenbaum had not been present, this likely would not have happened, either, but he had the right to protest. 

Mr. Grosskreutz had the right to be there also, may not have had the right to be armed (felon), and certainly violated basic firearm and personal safety concepts by pursuing and pointing his firearm at someone who felt he had to defend himself against ongoing attacks while attempting to retreat. 

Many choices were made by many people along the way for this event to end in a tragic and violent outcome.  Mr. Rittenhouse's decision occurred at the end of a long chain of related decisions.  Interrupt that chain anywhere and we would have seen a different outcome.