"One of the beauties of the human experience is that we can overcome our genetic "switches" to derive a more positive experience.
You're not a slave to your instincts unless you want to be."
That's old tabula rasa thinking - it's false. Tell that to someone who has fallen in love (another example of this type of genetically-programmed behavior) or who has bonded normally with their child. They'll laugh you out of the room. They would, in a heartbeat, throw you and themselves under a bus to save their loved one(s). They are slaves to their instincts.
Until the "switches" turn on, few (in modern society at least) realize/believe the switches are there! It isn't easy to counteract something internal that you have no belief in and have not experienced before. And it may be best (for the other, certainly) not to try.
Some say, for example, that romantic love isn't real. But romantic love is automatic and non-participatory: that is, your conscious self doesn't do the decision-making. And when you fall in love, every conscious system in your brain will be suborned to justify your automatic genetically-programmed behavior. So much for "free will!"
There are many instances where a parent does not bond with a child - they will not be protective or nurturing. In extreme instances they may kill the child. But none of this is normal or common.
Tabula rasa says there are no real switches. Grandparent is saying that there are, but we don't have to obey them unthinkingly.
Not all switches in the human brain are for stuff that's as nice as caring for children or falling in love, so you might still want to think twice before unquestioningly endorsing their superior wisdom over conscious thought.
How does he know that we can override genetic behaviors? Sure, we can try, but that doesn't mean that we can override them.
Given that you could view large parts of human culture as semi-successful overrides of instinctual behaviors, I'm not entirely sure what kind of thing your thinking of that might not be possible even in principle. Not feeling the instinctual impulses to begin with as opposed to not acting upon them?
You're not a slave to your instincts unless you want to be.