Without the benefits of gesture and inflexion (also the lack of visual cues from noting reactions in face to face interaction), it is very much left to the reader to infer meaning.
In text alone, language is quite inferior to adequately express oneself. This creates a sort of paradox within the mental health forum space where participants are often highly attuned to negative connotations (self worth, belonging, pleasing others), and some degree of accountability must rest with the reader to understand that posts are rarely made to deliberately chastise the individual for their predicament or beliefs. This also applies to those who empathise with how a post is received where replies in solidarity only result in degrading the potentially unwitting responder, and thus perpetuating the cycle.
Posing differing views is usually an attempt to provide another way to conceptualise a situation and rise above any sense of helplessness, and yet it is these differences that can lead the reader/recipient into feelings of deprecation.
For this reason, any perceived inappropriate posts should be directed to moderators and not pursued in the public environment. I reiterate that anonymity in responses would negate individual retribution (without absolving accountability). Sensitivity in replies is not limited to those seeking assistance and care should be taken to afford such respect regardless of context.
To remedy this, classifying posts (with simple color coding - light colors, pastel shade) can allow some control for the OP to select the intensity of outcomes sought to help meet expectations:
1] Reassurance (pink);
2] Comforting Support (blue);
3] Relevant Advice (green);
4] Options to try (orange);
5] even those seeking a Critical Response (duly qualified, naturally) to challenge their way of thinking (red);
Notwithstanding the above, I have never encountered any directly offensive replies. Although easily misdirected, some consideration of another's point of view (and right to hold such view) is the very nature of forum support, and simply recognising this attribute might even be regarded as part of the solution.