I often paddle alone. Its not for everyone but as with all rules ( less than 3 shouldn't be ) there are always exceptions to the rule.
I don't enjoy it as much as paddling with friends but it just requires a little risk management and the commonsense to paddle well within your limitations. Everyones limitations are personal and differ.
After 20 years of playboating at my local spot in everything from 4 meter composite C1's to 1.8 meter pieces of plastic fun I've pretty much worked out the risks in that place and I'm quite comfortable there.
Therefore the maths for me in that place is simple. I'm more likely to be killed or injured in a road traffic accident on the way there or back.
I rarely creek alone as there are more variables involved but have done.
Its worth noting that no mater how good your friends are sometime in class 4 and more increasingly in class 5 your on your own anyway. Your friends may be there setting rescue or running blue angel behind or in front of you. As any experienced paddler knows though there are places on the river that no human can get to and effect a rescue within 4-5 minutes or however long it takes you to drown.
Even when paddling in groups I treat every rapid in my mind as if I am alone.
This focuses me on knowing my line , my exit points, the possible hazards and who else's life I may risk should I make a balls of it.
In reality its all about the group and my function within it. How good the group dynamic is, am i doing my part in it's effectiveness in rescue situations and equally the level of banter to be enjoyed.
Its far from a black and white answere i'm afraid.
for example
A regular paddling friend of mine and I arrived at a creek (pushy class 4) in normal water to find it huge. A level rarely seen. Guessing that most of the eddies would be washed through we reckoned it would now be a pushy class 5.
None of our other regular paddling buddies were available to join us but others where.
We both agreed it was within our abilities but where not sure about the other possible paddlers. We knew for certain it was above some of them but they seemed to be happy to join us.
After some taught which included the option of just driving home. My friend and i decided it was safer for just the two of us to put on.
We decided the risks we may face trying to effect rescue on this continuous river with little egress far surpassed that of not having the extra bodies along.
ps. Kayaking funnell ? Now that taking it to a whole new level Joe. Waiting for the Rugby world cup to start too ( Come on ireland ) Might give that a go if ireland win