Most of the bees being kept by beekeepers aren't natural as such. One of the most common types is Buckfast and that's a cross between a number of different species. So is the suggestion that we kill 75% of the bees in apiaries to "keep it natural"?
Normally you also only buy one or two colonies, the rest of you apiary will be made from those original colonies and you only buy new ones in case of disease or if you want to build a larger apiary faster. So I don't get the negativity towards "buying bees online". While I do think swarm catching is great, I'd recommend getting the swarm checked for disease before placing it in any apiary.