If the seeds had no nutritional value the plant wouldn't need to protect them with poison.
If you read what I had said above, I said in most cases the seed would pass through the gut without being digested at all, and in that case, it would neither release its poisons, nor any nutritional component within it - so in that case, it does not need the poison.
The problem arises with animals that either chew the seeds, or whose stomach enzymes are capable of attacking the seeds. It is only in those cases that the poison is likely to be released.
The purpose of most fruits is to entice an animal to eat the fruit (which is full of nutrition for that purpose), to swallow the seeds whole, and then allow the seeds to pass through the digestive tract unharmed, and be deposited some distance away with the faeces of the animal. Clearly, if this goes according to plan, the last thing the plant wants is to poison the animal. On the other hand, if the wrong animal comes along, one that might cause harm to the seed as it eats the fruit, then there is good reason to use an effective deterrent to ensure that animal does not eat the seed.
Ofcourse, humans totally mess up the whole plan, because rather than depositing their faeces upon some fertile soil, they flush it down the toilette, and with it go the seeds.