Not quite sure what you mean.
If people want to try the beta in order to judge whether they want to purchase or not, then they preorder the beta find out its not for them then cancel their preorder and come September are suddenly charged without actually wanting the game. Then such a situation would suck.
Or you preorder now, intending to pay come September, and in the meantime loose your job and need to cut back where it's possible. Lots of situations where it could backfire as PSN is structured now, and Sony kinda need to address officially whether all these people will be charged come September or not.
that's all well and good for you, but folks who pre-ordered a physical copy (like i did from amazon) do not have access to pre-loading this. the obvious concern is that we'll miss out on precious beta time if the download is slow or bungie's site goes down on the 17th due to the huge amount of traffic it's sure to have. i'm sure the vast majority of people on here doing this are doing so for that reason, not to maliciously take advantage and get a free beta without pre-ordering
The download isn't a demo to help people decide whether they want to buy the game or not, it's a beta version of the game that is available to certain people because they've pre-orderd it via the PSN.
As the OP say states this guide was posted to "help" people who had pre-ordered it on PSN download it and they're the people who are going to have issues if they choose to cancel a pre-order that they want to keep and that there is genuinely no benefit in them cancelling as they can just download it the same way as every other PS4 pre-order.
When people pre-order it on the PSN they agree to a contract which means that Sony will withdrawal money from them even if they cancel it and they loose access to any additional content due to pre-ordering. When these people have access to that content removed from their account they have to understand that it could be removed from the account irrelevant of whether they also pre-orderd a disc copt of the game, it's possible that they could loose access to it on top of them having to claim a refund through Sony.
Once the contract has been accepted by people downloading a part of that, whether it;s the beta or anything else, legally Sony have no obligation to offer refunds because whoever has downloaded it has agreed the contract by downloading it.
Everything may be fine for people who mess around with it but it's risk that people need to consider before messing around with it and risking the things that could go wrong.
For people who have pre-orderd it via PSN, there's no reason at all to be cancelling the pre-order unless you don't want it any longer because you can download it using the standard way of downloading PS4 pre-orders.
Of course people can do whatever the hell they want but surely it's better that people understand what they could be getting into here. You only have to look at all the pre-order issues with Watch Dogs on PS4 for people pre-loaded a game that wasn't supposed to be pre-loaded.