Is the use of extracts in beer brewing a good thing?
It is actually quite common for commercial breweries to use hop extracts. Even Belgian Trappist breweries do it(!). And their beers are considered among the best in the world.
In my opinion it is not necessarily a detriment to good beer. Same thing with malt extract, from which you can actually make some damn good beer. But it won't give you the same flexibility as all-grain would.
The reason the big commercial breweries use them is because they strive for consistency -- and hop extract give them just that. It is very predictable. That said they do also put a lot of effort into making beer cost-efficiently. On a larger scale the little things have a big influence on cost. Note that the reason they aren't using malt extract is that it is much more expensive than all-grain, which lets them squeeze the last drop of malt sugars out themselves.
This shouldn't stop them from making good beer though, as there is no defense against making bad beer.