Welcome Derick!
Awesome that you saw Forks Over Knives! Great film.
Oh man, I don't know where to begin when it comes to people at the supplement shop. You're right, science is science. For someone to say that plants don't have complete protein, is to say that the Earth is flat. Seriously, I would consider those statements to be in the same category, simply because it is insane to say that plants don't contain complete protein, because many of them do.
And to suggest one can't build muscle on a plant-based diet would be admitting again that they don't have any idea how science and biochemistry work.
The problem is that most people think that way. Quite frankly, one of the primary reasons 80% of people in North America are sick. They all seem to think they know what is right and wrong nutritionally, but don't have a clue.
I'm taking a plant-based nutrition certification course right now through Cornell University and the more I learn about how the general public forms their ideas, the more frustrating it is.
Anyway, it's a longer conversation and almost 1AM and I still have some work to do before bed, but wanted to say welcome aboard, and please question those ideas about nutrition that the supplement store and trainer say. I would ask them if they have a background or understanding of science. No offense to them, it just seems very clear that they don't know how the human body and nutrition work.
See you on the forum.
All the very best with your health and fitness goals!
PS, I put on 75 pounds since becoming Vegan and won multiple bodybuilding competitions. You can mention that to them too

-Robert