These people just love their heritage and want to stand up for their culture!

No. Those people are more like the sovereign citizenship people in the US. They don't recognize the current state of Germany as the entity that succeeded the German Empire. Everything after it (Weimacher Republic, Nazi Germany and now the BRD) is deemed as "not legal" in their eyes.
As such they also don't accept some laws or police in general as the executive force of our government.

There are tons of other people who are proud of their history, heritage & culture without being a Reichsbürger.