Your question arises out of personal dilemma and difficulty in resolving issues to your own convincing level.
In my opinion it would be wrong to say that the question is opinion based. The question is a genuine one and intrigues many people who take their inputs from others and get confused while forming an opinion of their own.
I would suggest you to go thru the texts of Bhagwat Gita where the evaluation of dharma and adharma was explained to Arjuna by Sri Krishna. Killing someone who does not respect others (Shishupal) or intentionally hurts others is considered as dharma. Anything done for greed is also not dharma. Greed is a result of lack of control over the five senses which drives a person towards committing sins.
Killing of an animal by another animal is always due to their natural demand which is the eternal food cycle and hence never termed as adharma. Extending the logic of milk from cows (stealing it from the calf) can also be extended to Trees for their fruits as adharma.
Yes if you are born as and brought up as a non-vegetarian person then you can put yourself in the category the tiger who has to kill to live. Thus killing for basic living is not adharma. Biting by mosquitos is a part of mosquito's livelihood but hurting to you. So you reserve the right to get rid of them the either way. An act of self defence cannot be adharma.
But killing for pleasure of your eyes or the pleasure of your tongue is not dharma. Till the time you are controlling your senses and are caring for others so as not to draw any unjustified pleasure to fulfill the greed of your senses you would not commit any adharma. The moment your senses start controlling you and due to that you start hurting others (plant or animal either thing) you can term that as adharma.
As defined in the Bhagwat Gita a yogi is not the one who tries to 'suppress' his basic needs. The real yogi always tries to mould himself and control his senses such a way that either abundance or the lack of anything does not disturb him. A yogi feels the hunger and is aware of it but is able to control the body if he is not able to find food. He does not indulge into overeating as soon as he finds food in abundance.
The yogi as defined in Gita is the one who follows dharma. Hope this will fire your imagination further and help you draw your own conclusion.