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The only time you will scratch the glass is if you don't know how to use a scraper properly.
I do agree with you though and have seen results where people have gone mad with a scraper and scratched the glass
Paul
Even if you use a scraper properly( scrape in one direction and take the scraper of the glass to start again)on certain kinds of glass you can still leave scraches, examples of this would be tempered glass with fabricating debris or glass with a coating on the exterior surface