only when publicly accessible yes. but twitter recently disabled reading tweets without an account and bypassing that for web scraping could make it not legal
Depends very much on the terms in which the content is made available. It's more than a little over-zealous, but the Computer Fraud and Abuse Act technically makes any unauthorized access to a computer system illegal. If Twitter makes it explicitly known to you that you're not authorized to scrape them and you do it anyway, there is some potential liability.
The entire Twitter outage was caused by scraping from only four addresses in Texas? And instead of just blocking those four addresses at the border they implemented rate limits across the board? That sounds ... implausible.