I am an American and am in complete agreement on this point - "RTFM" (and related terms like "WTF?" and maybe even "FUBAR") seem to me to be lower-level cuss words - more of a moderate swear word, less than a full-blown offensive cursing.  
 Although some pepople react very negatively to these terms, my (thoroughly uneducated) guess is that those people would also react negatively to the more moderate alternative terms like "flaming", "frigging", "freaking", etc. and thus the use of "fucking" here overstates the strength of the term RTFM.