I agree with you, I'm sending my children to the local comp. But then I'm lucky, last year 90% of children got 5A - C and 30% of children got 5A - A. Therefore, I am in a fortunate position to be able to say this.
However, has I lived in the local town, in the catchment area where the 5A* - C was only 38%, the school has been in and out of special measures for the past 10 years at least (including converting to academy status), and even this stat is doubled what it was a few years ago, when the number of children who got their A - Cs was around the 20% mark, and children are bullied / laughed at / picked on for being bright or working hard, then I would vehemently disagree with you.
OP your views are naive if you think everyone sending their child to the state comp is going to solve the problem. Trouble is, with the school above, the catchment area is almost entirely lower cost housing, where people have fewer options. Hence, that school is never going to get better. I remember my parents moved so I wouldn't have to go to that particular school, and that was almost 30 years ago. It really has been that bad that long!
Every child deserves the best start / education, no-one should have to settle for a second rate education. We should all be doing more, not less, to get all our children the best education possible.
[sorry for the rant, I'm a teacher and passionate about such things!]