Fair point.
In the end StartEngine decides, within the limits of applicable law, what information it requires. Yes, it is a disincentive to ask a question - but ultimately if you are going to go ahead and invest, you will have to provide the information that StartEngine requires.
I can’t speak for the details of US securities law but here it simply isn’t legal to own shares anonymously. Of course you can hide an investment behind a deep, complex structure involving multiple entities and entity types - if you can be bothered - but those aren’t what they used to be anyway.
Putting that option aside, if you ultimately go ahead and invest, you will be required by US law to provide certain information.
So between StartEngine and US law, if you want to invest anonymously then you better get on the phone to your accountant in the “Cayman Islands”. 
Presumably StartEngine has been doing this for a while and attempts to find the optimal balance of false negatives and false positives. Perhaps you are right that that might not be optimised for the Purism customer base. (But then you can be a Purism investor without being a Purism customer.)
To make an analogy with email, do you abandon using a spam filter just because it isn’t 100% accurate?