Everything everyone says is "in their opinion." Why should they have to state it outright?
I'm not disputing your right to state your opinion and I don't care if you want to necro a thread to make some offhand remark.
I just thought I'd point out that there is a difference between making a declarative statement and an assertion of fact. It can help argument (and communication generally) to clarify which we intend if it may read ambiguously for others.