Nothing offensive about it.
It's just that you're not likely to encounter a cougar while out hiking and less likely to be attacked by one (unfortunate and highly publicized incidents in California aside).
If you were unfortunate enough to be attacked by a cougar a stout 4+ foot staff would allow you to fend off the animal better by striking it and thrusting at it with more effect than trying to stab it with a 4" knife. You just have to convince the predator that you're too much trouble as opposed to trying to kill it.
If you are hiking in cougar territory where attacks on humans have taken place then a larger blade, like the aforementioned 12" machete, would be more effective than a 4" knife.
As to the blackberry thicket, unless you were to roll down a hill and be tossed into one I can't see to much reason that you wouldn't just walk around. If you had to, for some reason, wade into one to get through, I've used a stout walking stick to "slash" a path through. The machete would be a better tool for that purpose as well and the knife would be wholly inadequate.
Get a machete, cut a good walking staff and carry a new folder and you're all set.