According to the scriptures you are not directly responsible for the killing of that animal because you didn't do it yourself. This is a difficult one. Certainly as lay people we do have choices over what we eat. There's been a big controversy about this ever since the time of the Buddha. Devadatta wanted the Buddha to make a rule so that everyone was vegetarian, and the Buddha refused to do so because he didn't want to put demands on the lay people about what foods they were supposed to prepare for the monks.
I look at it in a deeper way. I've gone through various "food trips", vegetarian, fruitarian etc., because of the natural tendency in me to analyze things and investigate into things. I found that it was very frustrating for me, because I didn't want to be part of killing, but giving up the different types of meat and fish and everything, and even going to one stage of trying to be fruitarian because you didn't have the need to dig the ground and all, it was very frustrating for me, because then I came to the fact of wearing clothes. I saw that beings die in the production of clothes, or to grow anything, and making the tools, and I started to look more deeply and saw that in this maze of material things, I wasn't going to get out of killing by changing my diet.
Even if you look at a needle, living beings are dying in the production of these things. In the growing of vegetables, the flooding of the fields, how many living beings die in the flooding of the fields. I knew someone who grew bananas, and bananas look fairly harmless, but in order to produce bananas, this farmer poisoned the birds. So it came to me that in all production of food there seems to be the destruction of living beings. I got pretty depressed for a while, thinking that it's impossible, there's too much Dukkha in this world. There's no ability to get out of this.
Then I met the Buddha's teaching and I realized that there is a way out of it, and that if we actually develop compassion at a high level and don't want to be part of the killing of living beings, then we'll dedicate ourselves to becoming enlightened. This way we don't seek a body that we need to support, that we need to shelter, because in the production of anything there is going to be death. Since I was still in the cycle of Samsara, then I dedicated myself to be as harmless as I can, and at least, give something back to the world, so that I'm not increasing the suffering of beings. Usually when I go to certain places, I will eat the diet of whatever is there, following the example of the Buddha, and feeling thankful and taking responsibility for the fact that I have a body and at the moment I have a desire to have this body. I haven't become enlightened, so I take responsibility for this, and that means I have to make a lot more good Kamma to balance some of the desires that keep me caught in the cycle of consuming.
So as far as creating a demand for meat, yes that's probably so, you are helping to create a demand, however it is not the same as directly killing the animal. I often say to people I'm a failed farmer. Some people don't understand me, the deeper spiritual aspect that I'm talking about. They go, "Oh, you gave up." No. I didn't give up, I went away from farming, understanding that it wasn't satisfactory for me because I didn't want to spray, I didn't want to be directly responsible for the killing of living beings to support this body. I wanted to be able to direct my attention towards something greater than this. So when I saw the amount of killing involved in being a farmer, not just in the production of meat, but also in the production of vegetables and fruit and everything, I decided that there had to be a different way to get out of the cycle of killing. It's not on the material level but on the mental and spiritual level. So yes, directly killing is considered more negative Kamma than consuming things that have already been killed.