You seem to be inconsistent in your usage of the term. Biological drive to over eat is like the biological drive to over breathe.
OK, so it appears you don't understand the range of biological drives that we have.
Do you call the drive to have sex, a biological drive, or do you have another name for it?
Do you think we have a biological drive to eat? To drink?
Are you convinced all biological drives fit our current world, or do you think it is possible evolution is slower than environmental changes that might eventually affect natural selection pressures?
Your concept of what a biological drive is, how weak or strong such drives are, and how well adapted said drives are to the current environment vs past environments these biological processes developed in, seems insufficient. I suggest you consider the range of biological drives humans have.
The second problem you are having here is the fact mechanisms of these drives are not as simple as you think. For example CO2 controls respiratory rate in healthy persons. Hypoxia leads to rapid breathing. The thing is, these mechanisms, heart rate, respiratory rate, blood pressure, blood vessel constriction and dilation are all involved here. The physiology which results in how the biological drive to breathe is expressed is incredibly complex.
When it comes to appetite, there are even more complicated factors which result in the biological drive to eat or stop eating. That doesn't mean such mechanisms are all under conscious psychological control. What the research is showing is that there is no biological mechanism that prevents weight gain the same way there is one that prevents losing weight. There are a number of mechanisms which trigger satiation, (meaning you feel full and stop eating), but this differs from a mechanism that prevents weight gain.
There does seem to be some people in the population who genetically do become uncomfortable when consuming enough calories to gain weight. This is different than the mechanisms of satiation I mentioned which make one feel full.
Appetite controls are also different from the mechanisms which lead to original weight gain. Not everyone gains excess weight and not everyone gains it at the same times throughout their lives. I haven't gotten into the mechanisms which cause people to gain weight initially because this is such a complex subject and because it is a separate issue from the biological drive which kicks in when people shed pounds.
http://scienceblogs.com/geneticfuture/2008/12/slender_yield_from_fat_gene_st.php
If the biological drive is to MAINTAIN current weight, then why are people getting more and more fat?
Hopefully repeating myself again and again will eventually register with you. The evidence suggests there is a biological drive which resists weight loss. This differs from what you are picturing as the mechanism which results in maintaining one's weight. (Maybe my use of the term, maintain weight, has been confusing because I've used it mostly to refer to not losing weight rather than using it to mean maintaining one's weight, neither going up or down.)
It is very common for people to maintain a certain weight set point for long periods of time. There are complex factors which result in this set point changing. The vast majority of the time the result is weight gain. But there are rare times people lose weight like when depression suppresses your appetite.
These mechanisms are not magic little switches like a simple neurotransmitter in a synapse. Instead a number of feedback loops and complex interactions of chemical messengers and nerve pathways are involved. Scientist thought they found a single 'switch' when they discovered Leptin. But it turned out Leptin was only a small part of the entire system.
The fact the system is complex doesn't negate the fact the evidence supports the conclusion one of the pieces in the system is a biological drive to prevent weight loss. It has been described as having a gas pedal but no brakes. In most people there is not the same mechanism preventing weight gain as is triggered when there is weight loss.
You need to verify your belief which I am telling you the evidence does not support. Have you even looked at much weight loss science recently? Why not see if you can't support your belief since you are so convinced I am wrong?