I would argue that ... physical health.
Arguing is not the correct response for the given extent question. To what degree doyou disagree with the statement? Totally? If yes, then you should have stated it. Remember that your English understanding skills are considered based on the validity of your response and opinion. You cannot argue without the measured response presentation first. That means,totally disagree first then use the arguement presentation as the supporting thisin statement. The result? A guaranteed clear extent response and clear opinion that will get a maximized TA score.
Those who are in favour ... clear benefits.
You disagree with the vegetarians so do not defend their point of view. The idea behind this discussion is to use 2 valid reasons that proves the vegetarian reasoning is incorrect. By defending their position, you alter the discussion requirement from single opinion to comparative. Rendering your opinion invalid since you are now uncertain of it due to this vegetarian agreement paragraph. You have created a confusing discussion that now lowers an otherwise good starting TA score. Remember, the instruction is for a single opinion discussion. No part of the original prompt required a comparative discussion.
You might not recieve a passing score due to the conflicting response format. You can only be scored for the parts supporting your opinion, which will not be enough to meet the minimum word requirement without an additional supporting paragraph.