I suppose everyone could tack on "IMO" when relevant to avoid ambiguity, but I imagine that'd get rather tiresome.
That doesn't solve the core issue: you're making an assertion without supporting it with any reasoning.
"Homoloveuality is wrong." is a strong, bold statement.
"In my opinion, homoloveuality is wrong." is a weak statement.
The reason the first is strong and the second is weak is because in the second one you're admitting that it's open to interpretation, whereas in the first you're making a declaration. You can't make declarations that are subject to opinion without supporting evidence, which is my point.
Anyway, if everyone tacked on "IMO" or whatever people would find themselves needing to expand on why because their statements would be weakened.