You ARE arguing this like a sophist, you know. All that means is you can use tricks of logic to make a weak case stronger - it doesn't make you right. It's like arguing that sons should be allowed to beat up their fathers. It can be argued to be the case (see Aristophanes), but that doesn't make the argument right. The thing is, your whole argument is based on a single concept that is a matter of your own opinion: that all life is equal, plant or animal. Without that, your entire argument becomes meaningless. And yet, I don't think you can justify that first, crucial, stance, more than by saying 'I believe', thus making your who argument rather opinion-based rather than reason. A tomato is not equal to an animal nor to human. Saying it does doesn't make it so. If I call a tail a leg, how many legs does a dog have? Four. Calling it a leg doesn't make it one. In the same way, saying that a tomato is an equal life to an animal does not make it so.
The thing is, I'm not heartlessly cruel to animals or anything. I detest spiders, but I won't kill them if I find them. Usually I'll just have them moved, or ignore them. But on the same note... okay, here, I've got the clincher for you Legend. A hypothetical example.
A man with a gun is standing forward, and in front of him are a man, a dog, and a pear. He says he will shoot one of them. The choice is yours which one. In that situation, would you seriously say 'it doesn't matter, they're all equal'? Or will you say 'the pear'. If it is just the man and a dog, would you say it doesn't matter, or would you go for the human life over the animal? And don't just start making things up now in order to keep with your argument. Tell me how you'd actually act - don't deceive yourself or me. And I would be willing to bet that you would say the man on all accounts. And as soon as you've done that, you've stratified the value of life, and placed it human-animal-plant. And, in doing so, you have annulled your argument. You might be arguing for equality but, as I said, you are arguing as a mere sophist - playing the devil's advocate. You don't really believe that, or if you think you do you've fooled yourself as well. The case you are making is really weak.