[gbalduzzi]

I think it depends on the definition of bad.

I always consider "good" a bot that doesn't disguise itself and follows the robots.txt rules. I may not consider good the final intent of the bot or the company behind it, but the crawler behaviour is fundamentally good.

Especially considering the fact that it is super easy to disguise a crawler and not follow the robots conventions

[atoav]

Well you as the person running a website can define unilaterally what you consider good and bad. You may want bots to crawl everything, nothing or (most likely) something inbetween. Then you judge bots based on those guidelines. You know like a solicitor that rings your bell that has a text above it saying "No solicitors", certain assumptions can be made about those who ignore it.