Ofcourse we do, what would be holding us back? Obviously our choices are mostly heavily influenced, but that doesn't mean we have no control over them.

If you continue with the OPs logic, one could argue that even those little actions could be attributed to external factors... Molecules ineracting, physical and chemical reactions, stimulating your itch reflex for instance

Pretty deep stuff :p

I think adding physiological functions/needs only complicates this discussion needlessly.

You need another option - to an extent.

Do we have free will? Yes, to an extent.

I agree, humans (like all other animals) probably don't have what we usually call "free will".
As far as I know, that's also the current state of knowledge in neurobiology/neurosciences.

Depends. What is free will?

Unless quantum mechanics can convince me otherwise, I'm going to continue thinking that the universe is deterministic, even if we can't know everything precisely enough to determine the future. However, free will is a sufficient model for our actions because in the end, our behaviour is too unpredictable.

More importantly, who cares? It's not like you can do anything about it and it's not like knowing the answer is going to change anything. I don't think it's a question worth sacrificing a lot of time to.

humans have free will, like the insects

plants and bacteria for example do not, it's so simple

My numerical system below is the method I'll be using to respond to the corresponding paragraph.  It's easier for me that way.

1. There are many external environmental factors that we have no control over and these present to us unique situations in which we respond.  That much I agree with.  But there are many possible responses to that situation, and this is where free will comes into play.  I am not certain how you are choosing to define free will--that in of itself is a subject of great debate--but I choose to define it as the capacity to act and react freely on our own will.  Willpower is a different thing entirely; I define it as the strength of one's motivation. Those with stronger willpower can overcome personal obstacles such as addiction easier than those with weaker willpower, but ultimately both have free will as they still have the capacity to choose.

When I am presented with a situation, depending on the amount of time at my disposal I can choose among the many options.  In the mundane world I can choose what I eat; I used to be a picky eater but trained myself to be more open and so I have more choices (among the foods I like) than before.  In more complex situations I may have to make ethical decisions I am not sure about, choose between unpleasant options in spite of their consequences, choose to react with emotion, reason, or instinct, etc.  Some people overcome their situations, others allow themselves to be defined by it.

2.  People are not born with the same states of mind.  Despite having the same atoms, they do not necessarily have the same molecules forming tissues in the same pattern.  Some regions of the brain are larger or smaller than others, and depending on the hormonal balance of the mother, the developing brain may be exposed to different levels of chemicals in certain zones, affecting its development.  And then there are genetic defects, fetal alcohol syndrome, hereditary diseases, etc.  All brains are very different but functionally similar to have a sameness.  If that's not a word, it is now.

The anatomy and physiology of the brain is an important starting point for the formation of one's personality.  For example, those with Fetal Alcohol Syndrome have a more difficult time restraining their aggressor response.  But the brain is only one factor of personality; one of four, to be precise.  The other three are memories, experiences (which are linked but distinct from one another) and personal choice.  Experiences present situations for us to respond.  Our brains influence our response but part of higher thinking allows us to go against what we know or what biology encourages us to do.  The end result may form a memory, which is imperfect and likely to change over time.

But the choices are the defining point of who we are.  Certain things we don't have choices on, like sexual preference, but they are a determinant on how we live, act, and treat one another.  And even then, at any time we have the option to reinvent ourselves if we reflect and decide that there has to be a change.

3.  Decisions are the response to a situation based on what we know and believe.  And we do choose what we perceive in many events.  We seek out knowledge and experiences, be it found in a library or a needle.  We can hear opposing opinions on a subject we know nothing about and ignore one of the argument, or more commonly, ignore a good idea because it's not our own.  We sometimes think we see things that aren't there, and often neglect to notice what's plainly in front of us. 

A decision is a commitment to an action or a belief, the possibilities limited to what we know.  That model may not apply to the criminally insane, but that's another matter entirely.  These possibilities or options may be limited, but they are still options and we may still choose among them.  The choice is still there, still available to be made freely.  Even when the other options seem so unthinkable that there doesn't seem to be any alternative, there is always the choice between action and inaction.

4.  I admit that choices are presented by and influenced by external factors, but they are not decided upon by external factors, and that's where choice comes in and choice is the instrument of free will.  And while our personalities may be affected as a result of these circumstances and decisions, we often make decisions contrary to what our personalities would dictate. 

5.  There are many prisoners who stemmed from stable, loving families that provided for them.  And there are many from the worst of circumstances who become paragons of society.  Conventional predictive models may be consistent within a certain standard deviation of the population, but there will always be those who stand that predictive model on its head simply because they had the personal motivation to do so. 

Conclusion: I find your argument demonstratively insufficient.  However, if you define free will differently than I then our discussions will be equally insufficient to one another. 

Um...yes we have free will.

How you ask?

We are not controlled by anything, except ourselves at the time we take decisions. Sure we have our past experience, but we still have a free will to either ignore our past or to consider it.

We have free will, hence. There's only a limited set of actions for certain functions, and humans tend to take the best course of action for themselves after they consider their knowledge base or whatever. They can do otherwise.