bad hacker rank tests are bad, but not all hacker rank tests are bad.
Could just say, for example, you don't think it's a disrespect to oneself to attend Hacker Rank tests and explain why.
There is an abundance of bad tests out there, but blanket statements that you won't use a tool that is used for assessing candiates is just as rediculas as saying you won't give apply to jobs that ask for your cv to apply.
Comparing it to a CV is a false equivalence because it takes me O(1) effort to make and CV and O(n) to do some stupid timed algorithm test for every company that is interested in the value of my labour.
There are many "in good faith" steps that both parties must do in the interview process, wherein if either party drops the ball it really makes sense for both parties to cut their losses and move on; which I believe is what you are getting at.
There is employment contract for a trial period, because you only know how good coder is when they face real problems/code. Writing sort algorithms on white board might look cool, but in real world you will search internet for best algorithms for your case, look up generic one, so you will not make a trivial error writing it from memory, or just use equivalent of std::sort.
I'd rather not work with people selected this way. There are plenty of companies using much better filtering processes.
You can call me whatever you'd like, but I'm a service provider and I have no obligation to offer my service to anyone.
Personally I like Hacker Rank and consider it a good way to learn about new algorithms but at the same time I do not like the style of interviews that require it and it makes me wish I could leave the industry because it's a waste of time for people with a lot of practical experience and who have a good portfolio of apps/sites they've created.
That said, I would recommend not doing DMCA at all unless it's really serious. Sounds like your company has a lot of problems with this. Think StackOverflow, there are plenty of sites that copy it but I'm not aware of them going after anyone. If anything all the copying of a site makes it more of an authoritative source because a lot of people reference it.