I can assure that we do try our very best to keep the cabin temperatures comfortable.
It can be difficult on some aircraft as they seem to have a mind of their own.
This is how it normally works.
On the 747 there are controls in the flight deck and in the CSD's office.The flight crew have control of the temperature while the aircraft is on the ground and for the first 20 minutes of the flight.After this they normally leave it for the cabin crew to control.
I along with most crew set the cabins to 23c as per Boeing's instructions.I set First Class to 22c as they have thicker blankets and duvets.The 777 is the same but also has a temperature control in each galley.The 767 is only controlled from the flight deck.
There is no conspiracy to keep our passengers at an uncomfortable temperature (what would be the point)however we do need you to tell us if you are to hot or cold, for us if we are working in the cabins it always feels hotter then it is for you.