Yeah functional languages do make it easier to protect from unintended side-effects. the average programmer just doesn't get functional languages tho - and the average program doesn't lend itself to functional programmes (by average program I mean line of business stuff)
I've been to a good number of places of employment over the years and disappointingly a lot of programmers are not super awesome. It's not so much the programmers that cause hte problem though, it's the constantly changing business demands and that often, especially in larger enterprises it seems the people calling the business shots are too ... errr. smart. --- at least, they don't understand the impact of what they say.