My opinion as a vet student...
Yes, those who have told you that it can be more dangerous to not have your dog's teeth cleaned are correct. Bacteria that build up on his teeth could potentially cause infections in other organs, such as the kidneys, heart, etc.
And yes, any anesthetic procedure has risks involved, but if you trust your veterinarian, and they are experienced, the risks will be minimal. Your vet should take a blood sample before the procedure to check the liver and kidney values for your dog. There are certain chemicals that will increase if the liver or kidney are not functioning well, and this is important to know, since these organs function in metabolizing the anesthetic drugs (getting them out of your dog's system). Of course, it is possible to have early liver or kidney disease that does not yet show up on a blood profile, but by having the bloodwork, the risks associated with anesthesia are minimalized.
If you're still worried about the procedure, I'd talk to your veterinarian. I'm sure they would be happy to explain things to you.
Also, my dog has had dental cleanings in the past, and has always done well even though she has an immune disorder and liver disease.