It is very far from a DDOS tool. Scraping can be done from a single source, one request at a time, with self imposed rate limits. Sure it can overwhelm a server, but then so can a single user opening 10 tabs.
That's not what this tool does though. It allows you to distribute your scraping to a layer of proxies. So, the only difference is whether there is an intent to do harm to the target or merely collect data... which could be a form of doing harm as well?
There's definetly an argument that dangerous tools should be regulated to varying degrees. If we're arguing regulations in this specific area you'd probably also be balancing it with regulations that sites can't close an account for reasonable rate automated access and that public research can have higher rates so long as they're not crippling.
I wouldn’t regulate this but If you’re introducing regulations, why not just require the source to deliver the data in a neatly packaged format? The necessity for scraping and the potential for DDOS and potentially nefarious behavior basically goes away.