This is an excellent post by @funbreaker about why Matrix is unsuitable as a communications tool.
@Edent @funbreaker looks like quite FUD.
There were abuse attacks in big public rooms sometime last year, but the anti-abuse tools have become much better and I haven't seen anything but few random spam DM's for months.
Perhaps the rooms in question are not moderated well and/or not protected by anti-abuse bot. Spam & abuse exist, but they are no longer a big problem like year ago.
For example Meowlnir is a great tool:
https://github.com/maunium/meowlnir