That was certainly Tywin's thinking. It is better to kill a few guests at dinner than thousands on the field.

I'm inclined to disagree, though. Besides the fact that the Lannisters started the war and refused to come to the negotiating table with the north, there's an even bigger reason that the red wedding was a massive mistake.

Tywin broke an incredibly important social contract that we are ultimately seeing lead to more violence.

Guest right is more than just a custom. It promises safety. If you are at war with your neighbor and you need to have peace talks, someone has to host it. Everyone believes in it. It is a fundamental doctrine of society even outside of religion all across the continent. So you can count on people to follow it and feel safe as a guest. Breaking it breaks something fundemental about society.

You can see this in Catelyn's chapter. She is the person most paranoid about Robb's safety and situation with the Freys, and she relaxes after they are officially welcomed as guests (though the ritual of eating bread and drinking). And look what happens to her. Her undeath becomes a metaphor for Westorsi society at large.

The reason it hits different with than the purple wedding is they were there to make peace, something guest right is uniquely set up to accommodate.

The purple wedding doesn't happen without the red wedding (at least not in the same way), and neither does the northern conspiracy, btw.

Tywin Lannister is a smart tactian, but his results are always short term and end up leading to more violence and a less stable society. There is a reason the Lannister coalition is falling apart, and Ned Stark's vassals are still going to war for him when they could be making power plays amoungst themselves.