1/n I'm thinking about starting up a daily reminder that a single rollup that everyone uses is dangerously insecure.

Why is that you ask? Yes, rollups are secure as long as one honest party is validating and making sure to challenge invalid blocks.

So then what's the problem?

2/n You've probably heard complaints about running Ethereum nodes today. Over time running nodes gets more difficult as the total size of the chain state grows.

An Ethereum with 10x the capacity would take 10x more resources to run. Soon end users wouldn't be able to validate

3/n This is where one of the weirder arguments comes in. The claim is made that since rollups only rely on having a single honest validator rather than 51% honest miners, it's ok for regular users to be unable to validate.

That totally misses the point...

4/n Do you think miners would be unable to validate if Ethereum was 10x larger? No of course not, they would just buy more expensive hardware.

The ability to run full nodes isn't important to stave off 51% attacks, it's important so that the system doesn't become centralized

5/n So is the situation any different for rollups? No. It's true that a single honest validator can force correctness, but if only a few people/companies in a world have the ability to validate, how much protection does that give you?

6/n You'd have to trust that one of those companies was correctly validating the chain, and there'd be no way to tell if they tried to steal funds since you wouldn't be able to validate the chain yourself.

That doesn't sound like the trustless L2 scaling I was promised

7/n A rollup chain must have a limited capacity if people want to validate it.

Ethereum has this too, it's the gas limit. If there are too many txes on the same rollup, you also need a gas market

If everyone is on the same rollup, you get high L2 gas costs, not scaling

7/n I'm lead developer of one of the main ORU projects out there, so there must be an upside somewhere, and I'll tell you what that is.

(Computational) Sharding

8/n Many different rollup chains can all be hosted on the same L1 blockchain. Each chain has an independent capacity and users only validate the chains that they're interested in

The total gas limit of all rollup chains can be close to infinite

9/n But what about composability? That's a valid question, and it's the biggest downside of rollups. Contracts need to be on the same chain to call each other

Developers will design tools to get around this in many cases. @ConnextNetwork is doing some awesome work there!

10/n It's likely that we'll have a DeFi mega chain, which will be cheaper than Ethereum today, but still have to deal with congestion

However anybody who can launch a contract in a less congested shard will have large amounts of capacity all to themselves

11/n That means that rollups can unlock all the blockchain use cases that have been priced out by the DeFi explosion while also increasing the capacity for DeFi contracts as well.

12/n Rollups aren't a cure-all solution for every problem. But they give us scaling today (soon™) without forcing us to compromise decentralization, censorship resistance, or security

13/n And if you can get by with limited composability, they really are a cure-all