Not a moral Bitcoin Maximalist. I don't say buying Bitcoin is any better for the world. Just that Bitcoin will be better than Altcoins as an investment. I said investment, meaning over the long term (plenty of short term trading opportunities in Altcoins)
One. Brand and network effects. Step outside the cryptoverse for a moment. Have any trouble explaining Bitcoin to a newby? Try Ethereum. Try hundreds of Altcoins. Building a crypto product/service? Building for Bitcoin is a no-brainer. Which Altcoin do you invest your R&D budget into?
Two. Not making any more of it. People fed up with money printing like land, gold...and Bitcoin. A big newbie question, but how can we believe "they" won't make more Bitcoin? Now ask that question of every Altcoin.
Three. Copy that. Sidechains will allow entrepreneurs to copy any feature of a cool Altcoin. Like Smart Contracts? Use Rootstock. Altcoins as a sandbox for experiments are a "good thing". As a donation to the community that is cool, as an investment thesis less so.
Four. Lightning Network. Sure we will also have Raiden on Ethereum. Raiden as an Enterprise IT tool is great, but that is very different from a true alternative currency for mainstream use; for that, see 1.
Five. Flight to safety from both directions. Coming from Fiat, Bitcoin is an Anti Fragile crash protection bet. Coming from Altcoins, Bitcoin is safe haven while still believing in Crypto. If you made millions in an ICO, where do you put your stash? No, really.
Ethereum is a wonderful technology innovation. It will be used by big corporations, but so what? If Proof of Stake really works, Ethereum could become a true public alternative currency because Proof Of Work is expensive. But that is like saying if we can easily transport solar energy we can get off fossil fuels - easier said than done. Casper in Etherum is still in development. Watch this space, this is a wild card.