What do we do with the billions of funds currently involved in meat production ?
How do those involved make a living if animals are no longer farmed ?
How will the animals themselves fare ?
Unless there is a profit to be made from farming them there is no incentive to look out for their welfare.
Soya growing currently is number 2 (or thereabouts) on the list of rainforest deforestation.
A vegetarian diet is only possible en masse due to the horrific air miles involved in worldwide transport and distribution of fruits and vegetables.
In many areas (and even countries) a healthy vegetarian lifestyle would be borderline impossible without those air miles.
Domestic crops and especially wild forage would be hammered to death and wild foods would suffer under the additional load if more people suddenly started down that path.
Local supply, not designed to cope with significant extra demand, could easily be decimated.
There are also those who argue that plants are capable of experiencing pain of sorts, or that they have 'memory' of parts that are harvested or removed. If that is ever proven then we're in for a world of trouble...
I am all for personal choice and only the luxury of the widespread availability of produce we currently enjoy allows us that option. In poorer countries I've noticed less incentive or tendency to take a moral stance when the main concern is having any supper at all, never mind a choice about what it might be.
Just a generation or so ago folks would look forward to an apple and an orange at Christmas, and bananas or a pineapple were considered a very rare treat.
How things have changed...
Take away the worldwide distribution of produce (and the awful air mile penalty that comes with it) and see how far most vegetarians will get drawing purely on local/domestic foodstuffs.
Britain (and most other western countries) is only a 'green and pleasant land' because it is managed.
There is no ideal solution.
On the subject of whether or not we should - until a solution is arrived at where the dietary requirements and personal preferences of meat eaters is met in full, where those involved with all aspects of animal farming, processing, distribution and sales can somehow be gainfully employed elsewhere, where the animals themselves are looked after until their natural demise despite offering no return, where the land continues to be well-managed, etc, etc, then those who wish to should. Those who prefer not to don't need to.
On the other side of the coin and since I am a big fan of wild meat and fish, I will have words with anyone who wants to deny me my hunting and fishing.
Now there's a moral can of worms for you to chew on