Is this what "child" support is for?

My ex...oh, wow. What a piece of work she is. Here are the facts: 1) I pay for my daughter's college and travel to and from college (13 hours away by car, 1 1/2 hours by plane; 2) I pay for my daughter's cell phone bill; 3) I pay for my daughter's health and dental insurance and bills and 50% of all medical costs; 4) I pay her a monthly allowance for living expenses; 5) I pay for my son's car insurance, 1/3rd of his car's purchase price, his cell phone and monthly bill, health and dental insurance and 50% of all medical costs. 6) I give my son a weekly allowance and often buy him gas for his car, etc and when he is not able to get regular work, cover his very expensive car insurance and buy him gas. 7) My son spends at least 1/3rd of his time with me, plus vacations, etc. We have a great relationship and spend alot of time together. 8) I pay my ex, ~21K a year in "child" support for my son who just turned 18 and will graduate soon. This is mandatory according to the child support guidelines of Illinois. The tax on this amount is already been taxed and the taxes paid by me and thus is the taxable equivalent of ~25-26K per year (depending on tax bracket). 9) My ex, who has a Master's degree and is certified in her profession, chooses to stay at home (my son is the last of her children) and do nothing. As far as I know she is not looking for work or seeking gainful employement.
So, when my son needed tires for his car recently, I asked my ex "Let's let him buy 2 (1/2) and you and I will buy one each.." Oh, she could not do that because she does not have a job. I noted that I was asking only for her to use $100-150 of her child support on him for this needed item. Again, she declined this offer.
She buys our son SOME clothes and makes him buy others. She never gives him an allowance that she had promised. She feeds him, yes. And, teenage boys can eat alot but there is no way all of this (some clothes and food) costs 21K per year! I am thoroughly convinced (for reasons I won't go into here but things she has told me) that her she and her husband are using child support to pay down their mortgage so they can retire early.
By the way, I have a teenage boy by my current marriage and I know for a fact we do not spend that kind of money on food, clothes, school supplies, etc. for him - my wife keeps track of these expenses and it is somewhere less than half of that.
Here is why I write about this...This illustrates so well what is wrong with the so-called "child" support system in Illinois. There is absolutely no accountability for what child support is spent for and it is not at all based on what the needs of the child are. Instead, it is based solely on income of the one paying the child support. I ask you, what kind of sense does this make??? Secondly, while "alimony" is not used anymore, most will agree that child support has become, in reality, alimony.
I am nearing the end of my obligation for child support and probably will shut this blog down when I am through. I will only say this: we need politicians who have a spine and will stand up for what is right. There is a dearth of such politicians.