That's fallacy one - assuming nobody notices the attack and realizes that if one coin falls, the next could too. You can't assume an unaware population. This isn't politics, people are paying attention because their money is on the line.
Also, in this scenario you're dumping a ton of money into the coin to make it die ... that provides a tremendous pressure to make it live.
> Again, side chains do _not_ scale with users.
This is a blanket statement that may apply to one or more pathological sidechains, but does not generalize.
The scaling of sidechains depends on the structure of the chain, trust requirements, and other usage decisions. This is utterly independent of what it's linked to, and only partly related to how often you link to the upstream chain.
> On a side chain, 10,000,000 transactions between 2 people costs $72 and takes ten minutes, but 2 transactions between 10,000,000 people costs $72,000,000 and takes over a month.
lmftfy - "On X sidechain design ...."