One of the things I have always hated to do is critiquing other authors' work.
Critiquing is a valuable experience which provides essential feedback to the developing writer, so it is not something which experienced authors can avoid in good conscience. However, critiquing a work, if it is done honestly, can be painful. You are complaining about someone's creative baby, after all. I can tell you from experience that being critiqued can make you doubt if you know what you're doing, of if you'll ever get it right.
What really hurts is when you have to critique someone who obviously hasn't got what it takes. My worst experience, one that soured me on critiquing for a long time, was an older gentleman who was functionally illiterate. I was dismayed by how bad it was: for example, he spent a whole page (single spaced) with the character arguing with a malfunctioning machine, yelling "No! No! No! No!" for line after line.
I gave up about a third of the way through, and had to go to that poor fellow, in the presence of all the others in the critique circle, and tell him as gently as I could that he simply wasn't a writer. It hurt him, and me.
The newby writer is a fragile creature. 100,000 words is a daunting challenge, and the skills often aren't there and have to be learned on the hoof. New authors need the critique process and the advice of experienced authors to hone their skills in a complex and subtle craft. But that budding talent can so easily be ruined by thoughtless critiques which plant the seeds of self doubt and rejection.
Snark, vindictiveness, and personal attacks have absolutely no place whatsoever in the critiquing process, and those who thoughtlessly engage in such do an injustice to the author and a disservice to the art form. Yet I have seen this repugnant behavior on several occasions, notably on individual blogs and web sites.
For the up-and-coming author, and even for experienced authors, critiquing is not only a valuable tool, it is also our duty to the art form to pass long our experience, provide a new perspective, and help the newcomer see what often gets lost in the repetitive drudgery of writing.
But to do so, the critic must develop a fine sense of balance - discussing the shortcomings candidly while maintaining a sense of optimism that the work as a whole is viable, but simply needs some adjustments.
One shouldn't dwell only on the negatives. Discuss the positives as well, particularly details which have been glossed over, and which could give the story a boost if properly developed. Maintain an attitude that 'this work isn't bad, it just hasn't been perfected yet'. Offer suggestions on how the story line or undeveloped details can be extended.
When dealing with negatives, show how those negatives can be turned around and made into positives. Discuss how characters (who are often two dimensional in early drafts) can be rounded into more interesting people. When pointing out logic bombs, discuss how those plot flaws can be amended, or used to advantage. Simply heaping on condemnation is the worst thing you can do. Guide the new writer to the light, rather than simply burying them in manure.
It's a delicate balancing act, and an important skill. Every author needs to develop this skill, and the conscience to use it wisely.
For further information on critiquing technique and standards, refer to The Author's Worksheet