Well more accurately, Blacks are only 12.2% of the population (not 17%) and in the last 10-12 years - not just picking the last year...shootings of Blacks by police has been very disproportionate to population. In fact in 2004, 2006 , 2008, and 2010 there were actually *more* Blacks shot than Whites. And the other years were usually around the 60/40 range. So for only 12% of the population to lead in being shot and in all years be far above 12% shot, it does raise some flags. Plus, most shootings of Whites are pretty clear cut cases where there isn't much question on the use of force. I don't think anyone is going to argue against police shooting a disgruntled guy who goes in a workplace shooting people. I'm talking about people who have their hands up or that get shot reaching for id after being asked for it, and those are the things that are happening way more along racial lines.
And although most police by and large are amazing, the Chicago Police in particular have a well documented history both recent and in the past 50 years of abuse. Read up a bit on them and it's pretty staggering. Police definitely have a tough job, and especially tough in the worst areas like Baltimore and parts of Chicago, Atlanta, LA, etc. But there has also been enough happen that I'm not going to blindly put blue goggles on and say anything they do is ok, and anyone they shot deserved it. Because we've seen cases with our own eyes where the shootings weren't justified, and without civilian video like we have today it would definitely be a your word against the police thing. Also, it doesn't help police credibility when half the time in these shootings they say their dash or body cams were off or that they just happened to not record. In 1 recent Chicago shooting the police even went in right after and forced a business to hand over their surveillance camera recordings of the shootings too, which were then conveniently erased. Just way too much cumulative shadiness to not look at these things a bit closer.