Some points:
- Many companies still send email without DMARC policies in their DNS. You'd be throwing away emails you ought to read.
- Why just no DMARC? Why aren't you also wanting to toss DMARC policies of p=none? What's the difference between, "I don't care, so I didn't set up a DMARC policy" and "I set up a DMARC policy so people stop complaining, but I turned it off because I don't care?" The result, for you, is identical. Spoofed emails will get delivered.
- A policy of p=quarantine is almost as bad. So spoofed email ends up in the spam folder along with a bunch of email that isn't a problem. We've been trained to not trust spam folders.
- If it isn't a policy of "reject" the email just can't be trusted is the bottom line.
- A lot of spam comes in from domains with a DMARC policy, even with a reject policy because the email passes the SPF check because it came from either their own email server or a compromised one or passes DKIM checks.
Your idea of tossing email without DMARC will not give you the results you hope for. You'll miss important emails, and you'll still get a steady flow of spam.
BTW, an extremely well-known cybersecurity expert's newsletter (Brian Krebs) goes out from a domain that is missing a DMARC policy! This just shows how not used it is.
I have checks in my email client and I put red tags on emails that aren't p=reject or that fail SPF or DKIM checks, so I'm extra careful. This is better than just tossing email with no DMARC policy.
I know this doesn't answer your question, but maybe you should think about whether you really want to do this.