First up, I have to say that I completely disagree that we should be analysing the chosen punishment here ignoring that Mark was already on two reprimands. The stewards will have known before they decided on what penalty to measure out that giving Mark a reprimand would generate a 10 place grid penalty. They did, therefore, in effect choose to give Mark a 10 place penalty, while only giving Fernando (who was 50% at fault) a reprimand that will probably not result in any form of actual penalty.
Anyway, putting that to one side:
Some form of punishment for both drivers clearly, and absolutely justified. Seeing that video: the way Fernando stops in the middle of the track on corner exit is dangerous. IMO deserves a penalty that is more than just a reprimand (especially if it's his first of the season, as it probably means he'll effectively go without punishment). Similarly, Webber putting himself at risk to go and jump on a car that's parked in the middle of the road was stupid and needed a punishment. But a reprimand isn't the right punishment here, especially knowing what the consequences of giving that reprimand would be.
This isn't what the reprimand system was originally brought in for (the other two Webber picked up are). Unfortunately I think the stewards are using the reprimands system as an easy way out, and have completely failed to consider the potential consequences of the way they've been haphazardly dishing them out. In Webber's case, at least one of his previous two reprimands was given as the "lenient" option, but has now unfortunately become a heavy-handed beat down.
Big financial penalty for both - big enough that it makes all of the drivers sit up and go "well, I'm never doing that then!"