Kortney said:
Of course they can.
"My opinion is that people from New Zealand all have three legs".
That's not true. Yet it can still be an opinion.
And the opinion (or '
belief') cannot be proven wrong. You can happily believe, or be of the opinion that persons from New Zealand all have three legs. You can have any number of weird reasons for believing this, none of which really matter (unless you're trying to persuade me).
The thing you believe in - the facts -
can be proven one way or another. In this case, we can look at Kiwis* and count their legs, and thus determine that they generally have two legs (or sometimes fewer). We can have definite
knowledge about this - an individual's legs can be counted.
But people
will interpret this knowledge differently, dependent on their personal experience, knowledge of statistics, level of sanity etc. - you might look at the data showing that 1000 Kiwis each have two legs and decide that it doesn't prove a thing, because you
know that all New Zealanders really have three.
The fact that no opinion can be categorically
wrong doesn't automatically make all opinions equally valid, though - a good opinion can be backed up by persuasive argument, at the very least (and possibly some facts and figures where appropriate).
Conversely a bad opinion is little more than the incoherent ravings of a lunatic (possibly backed up by something he's daubed across the wall in his own shit).
*'people from New Zealand', not 'small flightless birds' or 'little hairy fruit'
(tl;dr - opinions can be persuasive or nonsensical, but only the assertions or facts they're based on can be wrong or right)