grow what you want and pretty much ignore your friend. The exception to this would be growing corn next to a field of gmo corn or something similar.

The veggies you grow this year may be cross pollinated. This means seed saved from this years veggies may not produce true to type if you grow them next year.

The exception to this would be any crop where you consume the seed. Corn is a prime example. This is because the pollen that fertilized the seed becomes part of the seed which you consume.

You might look up xenia and metaxenia for some related information.

DarJones