You're right, that's a concern. The solution is to get everyone in the DNA database beforehand so there's no marginal cost of getting swabbed with a rape kit.
I'm getting strong Godwin's Law vibes from your response, btw.
Pre-collecting DNA from everyone to use as evidence against them in future criminal investigations is way over the line when it comes to “is this behaviour totalitarian or fascist”.
Using DNA from a rape kit to identify someone in a crime is a clear violation of the 5th amendment.
Just because you can do something doesn’t mean you should.
The majority vote can be rallied through fear and propaganda into vesting ever greater authority in a centralized seat of power, with any opposition vilified as an existential threat.
The only way democracy survives is through a watchful and untrusting populace that constantly holds its government to account and seeks to limit its power and pervasive reach into the lives of the citizenry.
Freedom and liberty require at its core the ability to dissent. Dissent in turn requires privacy because dissent by its very nature will be suppressed by those in power.
I would theorize that mandatory en masse DNA cataloging is anathema to democracy because it inevitably is far too powerful a tool to suppress dissent.
The next logical step if you don’t think the 5th was violated is collecting DNA from everyone (eg: repurposing COVID swabs) so you can identify all the potential suspects from your sampled population while completely ignoring that someone from outside the sampled population could be the person you are looking for.
Being able to positively identify people is a reasonable function of a government, including democratic governments.