My friend, you might want to read 'Flash Boys' by Michael Lewis.. Your perception would change regarding this topic.. Read it and tell me what you think.. It's a wonderful book.. Very informative..
I had only tried to scan information few months earlier to judge whether the book is worth it and from what i could gather its just another made-for-the-masses and consipricay-theory author. I could be wrong but anyway here and here are some reviews that maybe worth reading. There was more stuff but i dont want to search.
It seemed to me that author had many factually incorrect info in the book. HFT seems to have reduced slippage big time and driven market makers out.
Wont discuss anymore beyond this as i have not read / understood the subject and didnt find it worthwhile