One reason for income and funds requirements is that consulates want to know how solvent applicants are (to find out whether their plans are plausible and how likely they might be to work illegally or even choose not to return to their place of residence). That’s why consulates do not merely want to see some cash on hand but also assess an applicant’s financial situation over several months (income, etc.)
“Funds parking” implies getting money merely to disguise those circumstances. We are talking about money that is used to pad the account for a few days and would not even be available to the person during the trip. It’s really about defeating the whole process, which is after all intended to vet an applicant’s personal situation quite thoroughly. So you can’t expect the people who designed and manage this process to take that nicely.
Clearly people with no means, no income and no ties to their country (like a job or business…) are not particularly welcome in the UK and other rich countries. What consulates love to see is a stable job with a good income paid by bank transfer, something that shows without ambiguity you have enough money to make the trip and want to come back to your country. That’s not particularly “nice” but that’s the nature of the visa application process.
On the other hand, borrowing money from family is not forbidden per se but you still need to document your own income thoroughly and account for the sudden cash deposit. The problem here is that it looks a lot like you obtained money just to make yourself look richer than you really are and increase your chances of getting a visa. Also, the consulate wants to know that you (and your family) obtained the money legally, i.e. that you are not involved in criminal activities, money laundering, etc. And cash is much harder to trace so that’s another reason why large cash deposits are best avoided.
So it does not really make sense to claim that people “are free to do whatever they want with their bank account”. Simply said, they are not. If you want a visa, you have to submit yourself to a quite intrusive process and jump through many hoops. That’s not to say it’s pleasant or entirely fair but that’s the way the whole process is intended to work and the fact cash deposits are frowned upon is just one aspect of that larger process.
Incidentally, there is another subtle reason why getting money from family looks worse than you might think. In some countries, it’s not unheard of for a family to fund the education of its brightest children, hoping them to secure a visa to some European country, somehow get a better life there but also send money back. Even if that means starting from a student or visitor visa and looking for a way to secure another status or staying illegally in the country afterwards. And countries with restrictive immigration policies like the UK do not welcome that.
From this perspective, someone who already has money, kids they are leaving behind, etc. is a “low risk” applicant, they are most likely to be a regular tourist who will spend some money in the country and leave as planned. But someone who does not have a situation is more likely to be willing to try his or her luck any way they can. And because obtaining a visa and enough money to pay for the trip, etc. is not trivial, the rest of the family does expect something in return and you can be under a lot of pressure not to disappoint. For the consulate, the family loan you thought of as a harmless bit of help can therefore make you appear even more likely to violate the conditions of the visa.