I'm sorry, I have to argue with this, because it's the argument I hear most out of meat eaters as a vegan, and the one attitude that irks me most of all... plants do not have a central nervous system, and that's a fact. You need a central nervous system to feel pain. Therefore... plants do not feel pain. ;P
Do you have research to support this belief?
We presume that you need a central nervous system to feel pain, because we need a central nervous system to feel pain.
Human science is very human-centric. We make a lot of presumptions about things based on the human condition. Often, this presumption is based on our ability/inability to communicate with something. For the longest time, sharks and octopI were considered to be far from intelligent, because their thought process was so different from ours. However, they have since proven that they have great problem solving skills. I do not doubt that plants have a similar ability, though even more alien to our own method of thinking.
In the end, consuming anything causes harm to something. There is no way to get around this. Consuming plants causes less harm than consuming meat, but the pain is still there. Consuming minerals (if you could do such a thing and retrieve nutrients from it) does less harm than consuming plants, but the pain is still there.