It will cross-pollinate with your Heirloom tomatoes and then they will produce seed that is not true..............
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So what harm will the “untrue” seed do? Will the tomato turn into a monster? Shows us any actual injury that has resulted from other GMO crops.
Hello. Do you know nothing about genetics?
Your answer is in the part of RB's comment you copied and pasted.
Hybrids are usually sterile and if they do grow and bear fruit, they do not breed true.
If they do produce, it's closer to what the parent plant was.
They are a terrible choice for those wishing to save their own seed.
While it's true that hybrids can have better disease resistance and other advantages, their lack of breeding true is the issue.
Hybrids are a great way to get the general public hooked on having to buy seeds every year, and makes them dependent on others for their food supply, even if they want to grow their own.