Disclaimer: The following post is riddled with sarcasm. If you take offense easily then please leave now.

PLANTS ARE NOT CONSCIOUS BEINGS!!! They cannot experience pain, suffering, or have feelings. They have no nervous systems.
Now I'm far from an expert on this as biology isn't my expertise, but last I heard there was no concrete proof either way. There's an entire study of science that's working on figuring out if plants have these emotions or not. I would like to see your proof of why plants aren't conscious, who knows maybe in the next year they make a discovery that trees are really as intelligent as humans. Stating they have no nervous system based on animals makes them unable to feel the same things is a pretty blatant statement, especially since they are from an entire kingdom of species from animals and their entire body structures is vastly different.

Regardless plants are still alive. So why is it that one form of life should be regarded as better and kept alive while the other is allowed to be slaughtered?

Under that logic if the entire Amazon Forest (and for sake of this dilemma we'll say all the animal life was evacuated before hand) were set on fire to kill the plant life it would be perfectly fine because it's just emotionless plants by our definition of emotions, yet to set a gerbil on fire would be morally wrong because it has the physiology more similar to us. So where do you draw the line between where it's fine to kill one life for another.

And even if we are to suppose that plants have 'feelings' then it would still be wiser to eat plants, since fewer would have to 'suffer death' if people ate solely plants then raised meat.
A cow has enough meat to feed a good deal people. To equal that much food in plant life it would take dozens of plants harvested. Simple math here.

In our modern world, the continued use of animal products is actually holding us back rather then advancing, because the production of animal products consumes so many resources as to make it unsustainable.
Care to back this one with some empirical data? Cause I honestly don't believe this.

Raising animals is holding back civilization? Really now? It couldn't be something much simpler such as a flawed education system or a society that can still promote superstitious religions and actually work to hold back science or numerous other problems in the world. But it's gotta be a source of our food that's holding it all back....riiiight.

Also, animal production has created a legal way to continue the ancient practice of slavery through the trade of illegal immigrants who constitute a large number of slaughterhouse workers.
Legal? Last I checked slavery was illegal in pretty much every nation, namely the big ones where holding back civilization would be occurring.
But surely if we had no more slaughtering of animals that would solve the slavery issue, not like we have sex slaves or a majority of the slave population working fields and mines anyways. I mean the slavers surely aren't smart enough to just stick their slaves in another money operation if slaughter houses went out of business anyways right?

It was not the domestication of animals, which led to the progression of human civilization. Indeed, many stone age human tribes were capable of surgical techniques that the more 'advanced' humans of the middle ages were incapable of. It was the discovery of the domestication of high carbohydrate, high yield, high protein plants (wheat, barley, rice, soy, lentils, ect.), which catapulted human civilization at the end of the Ice Age. These first fields were actually dug by hand, and it was not for another few thousand years that people had domesticated cattle, which were not at first used for meat.
While your correct that working on harvesting plant life would help society grow by being able to stop chasing around herds of animals, you left out the fact they still didn't have substitutes for meat back then and would still need the protein that animals offered. Let alone the fact that progress would have been a lot slower if people didn't have horses to use for travel since all good vehicles required animal labor, it would have taken a LOT longer for people to travel and for ideas and goods to be exchanged. Not to mention there's only so far people can go on working on fields with human power alone before mechanical production, hence the simple fact that a few ox can till a field faster then humans.

Although you still make is sound like domestication is bad for the animals. It's not like people abused the animals, if they did then they wouldn't have very good workers if they beat or malnourished them. While I'm sure it did happen in some cases, the majority didn't. Better yet the animals were given safety, shelter, and more food then they would have gotten in the wild. I hardly see how that's a bad thing when all we ask of them is to pull around a few things. If not for us then all animals would sleep out in the rain and would be prone to predators attacking them.

Long post, but you just gave me so much to work with. Time for a rest while I let my brain get off overdrive.