Generally, rubber stamps are not in themselves bad or evil, but they have sinister connotations. After all, they are just wooden handheld devices uses to impress details on papers and other surfaces. I mean, what's negative about using a device to imprint. These negative connotations come from what people make of rubber stamps. 

In business and management, rubber stamps are a seal of approval when it appears on certain documents. The rubber stamp derives one of the negative connotations as embezzlement or corruption when it appears as a sign of approval on an inflated budget. Many questions such approval as if to say the rubber stamp decided to approve such evil by itself.  

Another bad connotation of the rubber stamp is that it kills people. This assertion comes from the fact that it was a significant seal of approval in the military. And for any war to commence with guns dispatched to military personnel, a rubber stamp must have appeared on several documents to allow it. So, this makes a rubber stamp have lots of blood tied to its name. So rubber stamp has a reputation for killing people. 

While these may be the negative connotations of rubber stamps but in the real sense of it, does rubber stamps embezzle funds? Definitely no. We can as well ask if rubber stamps kill people. Well, your guess is right as mine. The truth remains that it's not about the rubber stamp; it's about the people using it for such purposes. Rubber stamps are neither bad nor good. It all depends on the person using it.

Sometimes, these bad connotations may come from individual experience in situations where the rubber stamp was used to do something that brought about emotional pain. It maybe because of a delay or denial at crucial times resulting from the absence or inappropriate use of rubber stamps. The truth is, it still doesn't make it a bad tool because it's just a tool.  

Imagine someone taking the remains of a loved one to the morgue and was made to wait because the rubber stamp to certify that it was received was with someone who is not nearby. This makes the person wait until the authorized person shows up to stamp the document and receive the corpse. That may be the beginning of a bad connotation for a rubber stamp from that person's view. Some of these ominous connotations come from such experiences. 

It's not too good to focus on a side view of the rubber stamp. Apart from using it for bad things from which the connotations came from, how about the good things it is used for. What about using it to approve employee's promotion, approve treatment in the hospital, customer loyalty programs give away, etc. These are great things rubber stamps are used for, and it's cool if they also have connotations like lifesaver, advancement, etc. It doesn't have to be negative all the time.