The main complaint, at least publicly, was that F-type prisons would isolate the inmates from each other, making it easier for guards to brutalize them. Human rights organizations and European governments made this point. So did various prisoner advocacy groups inside Turkey, like the Detainees and Inmates Solidarity Association, and the Union of Inmate Families. The danger of guards beating up isolated prisoners was real enough. Problems of this sort exist in every jail from Baifra to Beverly Hills, and especially in developing countries like Turkey, where law enforcement officers are paid abysmal wages and prison conditions are low on everyone's list of public priorities.
Official brutality is definitely a problem inside Turkish prisons, no doubt about it.
But the opinions of human rights organizations and inmate families were of secondary importance. The gangs responded with hunger strikes. Self-Starvation Hunger strikes are not an unusual political weapon in Turkey. Labor unions use them, for example, as do other groups. Prisoners engage in them as well.