Most people don't think that pre-mines are reasonable at all. That's a good way to know which coins are scams. Why do they deserve 0.6% of a total market that could be worth billions of dollars, exactly? Because they changed a hash algorithm and released a marketing website?

That used to be the prevailing opinion. Pre-mined coins were generally regarded as scams or pump-and-dumps. But after Ethereum which is almost all pre-mined sharply rose in value, there seems to have been a change in public perception. This is what opened the gates for the new generation of altcoins, also known as ICOs. They don't pretend that they're anything else than pre-mined. In fact, the huge sums that the pre-mined coins are sold for is used for marketing as a measure of interest in their coin. It's a strange new world.

Why did Airbnb founders deserve X% of the shares of their company that could be worth billions of dollars? Because they made a stupid simple website to rent out your apartment? Same question, same answer. We live in a capitalistic world, I think it is reasonable that people try to launch for-profit ventures. Ethereum did something equivalent to a pre-mine + instant sale: they created the initial ETH supply out of thin air, and immediately sold it for BTC to investors.

Startups aren't comparable to cryptocurrencies. There is serious resistance to pre-mining in the cryptocurrency world.