Black Widow or Brown Recluse/Violin spider are definitely dangerous.
I hope I don't shock you all, but I would kill it. There are billions upon billions of spiders, and though they do help rid us of other insects, I certainly can't have my home full of cobwebs, either.
If I put them outside, they will only find their way back inside. They as well as many other of nature's wonders are in search or water, as well as shelter. In nature, they live and shelter underground, or in trees, which is just fine, but I can't save them all, nor do I have the time to do so.
If I find a Black Widow, or Brown Recluse (or Violin Spider as they are also known) they are hash. While few people actually die from the bit of the Black Widow, many in comparison die or lose limbs from the bite of the Brown Recluse/Violin spider.
The photo above is supposed to be a Brown Recluse/Violin spider. It may be, but other photos I have seen of these spiders actually have a pattern on their abdomen which very much resembles a violin, and I just do not see that same design here. Wikipedia states that they don't all have the same markings, and that there are other species which have similar markings, but that only the Brown Recluse spider has three pairs of eyes.
Wikipedia also states that these spiders do not live in California, but I know people who live in California and were bitten also in California, and diagnosed as having been bitten by the Brown Recluse spider. Maybe the diagnosis was wrong, but they did have serious bites, and also had necrosis of the bitten area as well.
The brown recluse spider or violin spider, Loxosceles reclusa, is a well-known member of the family Sicariidae (formerly placed in a family "Loxoscelidae").
Brown recluse spiders are usually between 6–20 mm (¼ in and ¾ in), but may grow larger. While typically light to medium brown, they range in color from cream-colored to dark brown or blackish gray. The cephalothorax and abdomen may not necessarily be the same color. These spiders usually have markings on the dorsal side of their cephalothorax, with a black line coming from it that looks like a violin with the neck of the violin pointing to the rear of the spider, resulting in the nicknames fiddleback spider, brown fiddler or violin spider.
The brown recluse spider has three pairs of eyes.
Since the violin pattern is not diagnostic, and other spiders may have similar markings (such as cellar spiders and pirate spiders), for purposes of identification it is imperative to examine the eyes. Differing from most spiders, which have eight eyes, recluse spiders have six eyes arranged in pairs (dyads) with one median pair and two lateral pairs. Only a few other spiders have three pairs of eyes arranged in this way (e.g., scytodids), and recluses can be distinguished from these as there are no coloration patterns on the abdomen or legs, which lack spines.
The abdomen is covered with bushy short hairs. The leg joints may appear to be a slightly lighter color.