Illinois income taxes are currently at a low flat rate 3%, though. That's lower than the income taxes in Louisiana, Mississippi, and Alabama (although these taxes are graduated instead of flat). It's MUCH less than surrounding Midwest states like Wisconsin, Iowa, and Ohio.
Most of Illinois' budget currently comes from corporate taxes, which aren't changing, and those are the ones that would affect the banks and exchanges. Property taxes are also pretty steep, with the exception of the City of Chicago which has maintained low property tax rates but high sales tax.
Guide to State Tax Rates
I'm not a huge fan of heavy government spending and entitlements, but even if you want small government, it's exceedingly cruel to suddenly cut millions of people off from important medical care and housing subsidies without any time to adjust. Since Illinois needs to balance the budget, a tax hike is inevitable. It has a sunset provision after 3 years anyway, so legislators will have to vote to renew it.
Low taxes matter when there's plenty of growth, and economic success depends on keeping people and businesses in your state, and attracting as many new ones as possible. When there's no growth, having a functional government is more important.