Eating meat and buying meat Buddha said to his disciples (monks), meat can be eaten if they are not seen, heard or suspected to have been killed on purpose for a monk. Eating meat is different from killing animal, it's clear.

Lay people on the other side do not obtain meat like monks do, lay people buy meat. The money then goes to meat seller and abattoir. Is this the same as "Causing another to kill"?
Buddhist ethics is the basis to develop wisdom and mastery over the mind. If there are no unwholesome Karmic results you cannot collect your mind to develop concentration as wholesome results give present experiences than unpleasant which is more distracting in meditation.

In the above case through you can argue that you remote form of indirectly kill in buying meat you do not create the type unwholesome roots associated with killing in the mind which results in unpleasant experiences later. Making others kills which has Karmic repercussion would be instead of you killing you order someone else to kill or bring hims to such a state that he will kill intending that he would kill.

Leaving aside killing, if you take ethics too far then you cannot live. E.g. your food and drinks do have microbes. Antibiotics kill microbes. I have heard once a monk with supernormal powers, after filtering water, saw that there were beings too small to be seen by the naked eye still in the water hence if you are strictly not to harm the you cannot ever eat or drink. The advice received was do not use your Jhanic powers to see if there are microbes in the water.

If you are vegetarian well and good, but if you are not, this is not a hindrance to develop mastery over the mind or wisdom and such action does not have karmic repercussions.