For me, this is about ensuring that all 100 companies play along the same rules. If, while following the same rule book, 10 are significantly more successful than the others, fine. If another 20 are significantly less successful, also fine.
What is no fine, is having some companies be exceptionally successful by breaking some rules. Think insider trading, it's a highly profitable business for those risking it, but has a long term negative impact on the market. Therefore we, as a society, via our proxy, the government, decided to enforce rules forbidding insider trading.
The above answers who. This leaves the question of sensibility, I am afraid there will hardly every be consensus on what is sensible or not within a diverse enough group of people. If you'd ask a bunch of investment bankers about sensible rules for banking regulation, I'd assume you'd get quite a different answer than by asking a bunch of consumer rights activists. Our current solution to this problem of finally arriving at a single "sensible" rule is the democratic process / parliament. I guess most would agree this process seems to be sub-optimal, but it seems there are not too many other options on the table.