The issue I take to this is that you must have a recognized title to claim knowledge.
This has two problems:
1. People outside of a group of recognition have unnecessary difficulty giving input. This degrades the "public" aspect of the forum.
2. Common words like "engineer" are redefined to have more authority than they do outside the forum. This means that those with broad engineering expertise and knowledge that is applicable to the subject are considered to not have any applicable knowledge or expertise.
It may be reasonable to require credentials from someone who is doing the engineering, or someone who makes final decisions.
It is not reasonable to require credentials from everyone who uses a noun to describe him or herself.
If you want credentials from someone who claims to be an engineer, then you can ask for them. Credentials need not be assumed.
There are positions like MD, EMT, Police Officer, etc. that do imply credentials. These titles inherently require trust and respect, so claiming one without credentials is fraudulent. "Engineer" does not fit into that category.