"Cruciferous vegetables are vegetables of the family Brassicaceae ..." 
We mostly think of food sources as being variations on the cabbage theme:
- Brussel sprouts
- broccoli - & rabe
- cabbage - including savoy, red, napa, etc.
- greens - various, including turnip, mustard, etc.
- bok choy
... but it also includes roots:
... & seeds:
- mustard - various
... & cress - particularly watercress.
As might be imagined, the phytochemical content varies in amount & breakdown.
As with perhaps all plant polyphenols, the role in the plant is to protect against environmental insult. Of interest are the glucosinolates. As the name suggests, glucosinolates have a glucose component; & the chemical is inactive when bound to it. An enzyme in the myrosinase  family is needed to cleave the glucose structure & release (activate) the chemical. Myrosinase is separated from glucosinolates in the cell & physical damage is required to bring them together - such as that inflicted by grazing animals.
It's possible that a raw fooder might enjoy sinking his teeth into a head of uncooked broccoli, but I could never do it. Unfortuately, heat destroys myrosinase, & stomach acid is ineffective at releasing the active chemicals.
For those foods normally eaten raw, it is important to chew thoroughly. I suspect that my teeth liberate only a small percentage of the chemical in a watercress leaf.
One must suppose that supplements in glucosinolate form are useless unless myrosinase has been added. After years of being on the market, Jarrow quietly added myrosinase to BroccoMax.
A British researcher suggested adding raw horseradish (for its myrosinase) to cooked broccoli. Good idea - she should try it out for a month. Perhaps her kids will love it.
For every food type there are some who disapprove & others who are committed to the food & will not listen to criticism. But food does not want to be eaten, & antinutrients are common. In the case of cruciferae:
"Cruciferous vegetables can potentially be goitrogenic (inducing goiter formation). They contain enzymes that interfere with the formation of thyroid hormone in people with iodine deficiency. Cooking for 30 minutes significantly reduces the amount of goitrogens and nitriles. At high intake of crucifers, the goitrogens inhibit the incorporation of iodine into thyroid hormone and also the transfer of iodine into milk by the mammary gland." 
Per capita consumption of fresh broccoli in the United States reached a high of 6.4 pounds in 2013.  One can only guess at average consumption for those who actually eat it. But whatever it is, I haven't seen a goiter in 60 years. If it were a significant issue, word would have leaked out. On the other hand, those with thyroid problems might want to do further research.
The next posts in this series will be:
- "Foods/Supplements-Vitamins: Cruciferous Phytochemicals -  Indole-3-carbinol [I3C]"
- "Foods/Supplements-Vitamins: Cruciferous Phytochemicals -  3,3'-Diindolylmethane [DIM]"
- "Foods/Supplements-Vitamins: Cruciferous Phytochemicals -  Phenethyl isothiocyanate [PEITC]"
- "Foods/Supplements-Vitamins: Cruciferous Phytochemicals -  Sulforaphane"