Why is forcing food down your guest's throat acceptable?  For some reason, it is considered polite amongst society, while I view this as nothing more than a giant hassle.

I realize when someone hosts a guest they want to make them feel comfortable, and one way to do this is by providing ample food.  Cooking a nice meal is always appreciated as a guest, but I have issues with the usual verbal jousting over seconds that inevitably arises:

Host:  Here, have some more.

Guest:  No thank you, you have already been too kind in providing a great meal.

Host:  Nonsense, you are just being polite, here have some more.

Guest:  No really, you have already done too much.

Host:  Please, have more [slops seconds on to their plates]

First of all, I find these conversations as being utterly fickle, as both people are simply playing out a scene with the ending already known.  So why do people have to put on this performance?  More importantly, what if the guest really doesn't want seconds [I rarely have a large appetite, therefore tend to shy away from seconds], the host is essentially forcing their guest to eat their food.  Why on earth is this considered polite?  Perhaps, they ate on the road, perhaps they are vegetarian, perhaps they don't really like your food, perhaps they are trying to lose weight, perhaps they don't like a particular spice, there are a large swath of viable reasons a guest may not want seconds, but the host is compelled to disregard whatever objections the guest has, instead imposing their own will upon the guest.  Again, how is this polite?

Sure the guest may simply not want to be an imposition, thus preventing themselves from being a hassle with a second or third helping of dinner/breakfast/whatever, but why is it considered impolite for them to agree to seconds upon being offered.  It makes no sense, and this is a social convention I feel needs to be changed.

From now on, if you are a guest and you want seconds, do not participate in the farce of saying no thank you.  If you are the host, please, listen and respect the wishes of your guest.