With regard to music bringing a lot of opinions to the floor, with few people showcasing what they themselves can achieve, I don't find it unreasonable to suggest that backing up your thoughts and criticisms with evidence of your own facility with sample libraries is such a bad thing.
Would you hire a 400 pound couch potato to be a personal trainer?
Would you cross a bridge designed by someone whose engineer training was comprised of watching "the greatest bridges in the world" videos on youtube?
Would you trust a pharmacist who told you the "pink pills are for girls and the blue pills are for boys."
Basically, what I'm saying is that, if you scour interet forums on music, the sheer number of opinions by so many anonymous individuals does require a way to ascertain the value of said opinion. In any other field, asking an individual for their credentials, experiences, and evidence of their accomplishments is perfectly normal. Ask a musician to showcase their musical output, and they suddenly get offended, call others names, and/or suggest that they're a snob/snooty, etc. At this point, I would vouch for the opinion on a library by one competent (as in their music illustrates their competence) individual over a hundred anonymous points of view from those who are too afraid to put their stuff out there for scrutiny.
Just my opinion, and no, I'm not exclusively suggesting that you can't have an opinion without doing something yourself, just that backing up your credentials with evidence of your own achievement will go further to reinforcing your point of view.
Really, just to drive the point home: would you buy any library by any developer without demos of the sounds? Why then is it so offensive to ask for evidence of your own musical output to determine the value of your opinion, even if the individual assessing that value is doing so purely in a subjective way?