Would the world be better off without agriculture?

It is estimated that under theoretically ideal conditions around 100 hectares of suitably planted land is required to support 1 hunter-gatherer person, which means that if we discount all the unsuitable land (deserts, mountains, swamps and permafrosted areas) then the planet could feasible support a total of 130 63 million people (though in reality probably less because that doesn't fully take into account the area of land and its ecology needed to support the fauna we would be hunting). 

This means that Planet Earth can support the population of Mexico The United Kingdom and the rest of us you would have to find 53 other Earth-like planets to colonise. We You could of course simply die out but then those 130 63 million survivors would have to dispose of 7 billion corpses without contaminating the land they need to live off. However, that assumes that the surviving population could be equally distributed across the whole planet, which isn't the case because physical geography isn't that amenable to such plans. For those of us living in the UK this means that the population would have to drop from 64 million to around 61 thousand so each of us who survives (and I do fully intend to be one of the survivors btw) would have to contend with disposing of 1,000 dead bodies per person, which given that to survive we'd need to group together in extended family groups (or tribes) of say 10 people each, would mean burying or burning 10,000 corpses in such a way as to prevent disease and other unfavourable environmental contaminations that would result from the subsequent increase in scavenger population. 

A tribe of 10 hunter-gatherers requires 1000 hectares of land (15 square miles) so our nearest neighbours would be roughly 2 miles away in each direction which means that defending our hunting and gathering rights from them would be tantamount to impossible, therefore the practical land area required to support 10 people is probably double the theoretical area so the total world population could be as low as 65 32 million, which in turn halves the population density.

This is before we start to consider the issue of a regular and reliable clean water supply, which again could double the area needed to support a population of 10 people so the total world population reduces to 32 16 million and your nearest neighbour group is at least 4 miles away. This is still 8 4 times greater than the world population from Palaeolithic era so land-area alone is not the sole determining factor.

And of course your neighbour killing you is the least of your worries as the environment also has you on its hit list but with far more belligerence - most living things really do not want to be eaten and go to great lengths to avoid being eaten. A palaeolithic landscape has a lot of fauna and flora but very little of it is edible and most of it is toxic so unless you are well versed in botany and mycology your first berry and mushroom stew stands an astronomically high probability of either killing you or making you so violently ill that you'll be unable to forage for enough food to survive. Also what is edible has a low nutritional value so you have to eat lots of it, including all those things that to modern tastes are unpalatable, we also have to remember that all the basic staple foodstuffs we consume (seeds, grains and root tubers) have to be extensively processed before we can digest them. 

This also means that lifestyle diets are a no-no, but that's less of an issue since all vegetarians and vegans would have perished with the 7 billion who did not survive the cull as the environment cannot support a gatherer-only diet. The human body requires more calories per day than can be gathered in one day because all those natural staples have a low calorific value, which is why we have teeth and digestive system for an omnivorous diet - basically this means that you'll not be given extra rations of stewed dandelion leaves and horseradish root just because you can't eat an ickle bunny wabbit - you either eat the same as the rest of us or you die. But not to worry, all those with food allergies also perished along the way too (sorry - but I did say I fully intended to be one of the survivors).