The problem is not just that the original author puts backdoors into scripts - other people may come along, take his/her script, add a backdoor or three, and then package it up and distribute it to look like the harmless original. LookSharp and Polaris are fairly well known for this, for example.
Another problem is that many scripts include far too much advertising for themselves (in quit messages, away messages etc.). Others go as far as having a default onjoin message - an advert sent automatically to everyone joining a channel with the user (Dynamirc was a particularly nasty case of this). All of these superficially harmless "features" (spam) get on people's nerves, and lead to the script being called "lame" - because it is! A good script will be used widely without needing to resort to the advertising - Peace & Protection is a good example.
Other scripts, of course, are annoying as hell for other reasons - Simpson Script and Vision send a colourful Italian greeting to every channel when they join. Not surprisingly, people get upset by this, and I even know of Italian channels that ban users of them.
Then there are also scripts which are mainly for (a) file trading or (b) retro games, looked down on by those users who prefer to use IRC for its intended purpose (chat!). And last but not least, there are the so-called "war scripts", for the wannabe script kiddies out there; the reasons for their unpopularity are obvious.
So... there are lots of ways in which a script can become known as lame and/or stupid!
At the end of the day, though, the old cliché that "the best script is the one you wrote yourself" will probably be true - because if you write it yourself, you will understand it, you can trust it completely, and it will do exactly what YOU need it to do (every user has different needs).
PM