Counselor: Constantly comparing oneself to those one sees as more able or more successful almost invariably leads to self-disparagement.
Conclusion (So)
People who mostly refrain from comparing themselves to others will most likely be self-accepting and accepting of others.
Evidence
Constantly comparing to people you think are better than you leads to self-disparagement (self-loathing / disappointment in yourself).
Constantly comparing to people you think are worse than you almost always leads to being dismissive of others.
Evaluate
This seems to be a "soft" version of the #1 famous flaw, confusing Necessary / Sufficient (which basically means thinking about conditional logic in an illegal backwards or opposite fashion).
These two premises aren't true conditionals because they don't convey certain connections (almost invariably), but they certainly qualify as Most statements (almost invariably is definitely more than 50% .... it doesn't have an exact quantitative threshold like Most does, but it's definitely over 90%).
Most statements cannot be read backwards or in opposite fashion either.
Most Senators are men does not imply that Most men are Senators. Most Senators are right-handed does not imply that Most people who are not Senators are not right-handed.
Let's pretend these premises were conditional just to illustrate the reasoning error:
Premise 1: compare to superior people → hate yourself Premise 2: compare to inferior people → dismissive of others
Conclusion: don't compare → don't hate yourself not dismissive
The idea of being "self-accepting" is meant as a logical opposite for "self-disparaging". The idea of being "accepting of others" is meant as a logical opposite for being "dismissive of others".
Goal
We don't really want an answer to say Necessary vs. Sufficient, since these weren't conditional premises, but we can use similar language to describe the flaw.
The argument assumes that because two things (comparing yourself to people better or worse than you) usually results in a certain effect (disparaging yourself or being dismissive to others), if you were to avoid those two things, you would avoid those effects.
But what if some other part of your life still causes you to be self-disparaging or dismissive of others? Comparing yourself to others was an action that was almost-guaranteed to result in X or Y, but this argument is acting like Comparing yourself to others is practically the only threat you have of being X or Y.