This comic was posted a day early, and has a sketchbook sibling as a result.
Constructive criticism is important for anyone to grow, be it as a person, professional, hobbyist, etc. I often receive criticism, constructive or otherwise, and it's helped me improve. This has included harsh truths from both polite and rude sources, and while I may not have liked hearing it (particularly from the rude sources), it has overall been invaluable.
So what's up with panel four? Frankly, it's inspired by several people I've encountered, both online and off, who don't seem to realize the value of politeness, or simply don't care. People who seem to believe that their advice should be cherished by all regardless of how they present it, and that those who fail to cherish it are arrogant.
These people are usually right about at least one thing, and that is that their advice, if good, should be listened to regardless of how they present it. The problem is that part of how we value bits of advice is by evaluating their sources, and if all one really knows about the source is a) the advice they've given and b) how they've presented it, the rude approach is full of problems.
First off, I consider what I'm about to say a matter of common sense. When talking to someone, being offensive is likely to put them on the defensive. Someone on the defensive is less likely to be receptive to the ideas conveyed by the individual or individuals who put them on the defensive. Therefore, when trying to persuade someone, it is usually best not to be rude. This is particularly true if one person is not familiar with the other, hence why this comic makes note of "strangers and casual acquaintances".
When someone I don't know well goes about giving criticism in a rude manner, it makes me suspect one of two things: they are unaware of this bit of common sense, or they don't care. The latter conclusion leads me to believe they're arrogant and possibly full of themselves, trying to get under my skin, or both. None of these conclusions make me confidant about their advice.
Now, if I know someone well enough, it's less of an issue. If certain friends of mine gave rude criticism, I would shake my head, say "that's my pal!", and the studio audience would clap wildly as I considered what they had to say.
If, however, someone is a complete stranger who is perhaps, I don't know, e-mailing me, and the first impression they make is that of a rude jerk? It's extremely unlikely I will consider whatever they have to say worthwhile, and I will most likely not finish reading it. Life is too short to waste on internet jerks, and if whoever was e-mailing me really was trying to give good advice, well... I'm sorry, but for the reasons I've listed, I'm not sure it's advice I would have wanted anyway.