It is acceptable if someone says s/he is telling true(own) opinion. No arguments about that. But how can YOU say "Many of the members here post their OWN OPINION". "Many" is larger than "few". So if the forum has 100 members (including newbies)"many" means 51 or more!.
Therefore, my argument is that, to make the statement "Many of the members here post their OWN OPINION", YOU should know answers for at least two questions.
1. How many members are there in the forum?
2. Out of that how many make the true (own) opinion?
If you do not know the answers for these two questions YOU can't make above statement.
In a online forum like this where no one knows others true identity, how can you came to know whether they are telling own opinion or not without knowing them (so without knowing their intention of posting here)?
The only way this can happen is either
i. Majority of members in this forum are from one particular organization or group of fiends, or
ii. Though there are different user names most of them belongs to one person or group of persons, so they) know whether they are telling the truth (own) opinion or not.
If neither i nor ii above conditions holds YOU can't answer above questions 1 and 2.
I'm sure you don't accept above conditions i and ii.
On the other hand, if you reject i and ii YOU can't make the statement "Many of the members here post their OWN OPINION".
Then making such a statement you have shown YOU ARE LYING.
Any defend/counter argument warmly welcome!!