First, let me state that I believe i am qualified to offer an opinion because I am a practicing biochemist and can more easily find and perhaps understand the data out there. However, I am not an expert on safrole or safrole metabolism, so do not take my word as gospel. I encourage you to look at the data and decide for yourself.
I think the safrole health hazards have been significantly overblown. Take a look at these two sources (one a secondary source, the other primary):
In the first page, the TD_50 dose of safrole, that is, the daily dose of safrole required to induce tumors in half of animals that would be otherwise healthy is 441mg/kg in rats and 51.3mg/kg in mice. The mg/kg unit means mg given to the animal per kg of it's own body weight. (e.g. 1mg/kg means a 1kg rat gets 1mg a day, a 2kg rat gets 2mg, etc) On the second link, liver damage is induced by daily dosing of safrole to rats, but it isn't statistically significant until 1000mg/kg doses are used.
Note that the mice and rat toxicity levels are quite different. Since the studies haven't been done on humans, we can't know exactly what the toxicity levels in us are. I suspect they are somewhere in between, but to be cautious, I will assume things are as toxic in humans as mice.
I am a person of average weight at just under 75kg. That means, to get a dose equal to that of mice I would have to consume 51.3mg * 75 = 3847.5mg a day (3.85g after rounding).
Let's say that I drink 1 of my own rootbeers per day. In order to have a 50% chance of cancer, I'd have to have 3.85g of safrole per root beer. Since my batches are 5 gallons (~50 beers), that would mean I'd have to get 192.5g of safrole out of the sassafras I seep. I start with 16oz (1lb) of sassafras root. Well, 1lb is actually only 453g. 192.5g/453g is 42%.
That means that my sassafras would have to be 42% safrole in order to even possibly extract that much
I can absolutely say that is not the case. Wikipedia, citing the Merck chemical index, says sassafras is 'a few percent steam volatile oil, of which 75% is safrole'. A few percent (3%) * 75% = 2.25%. Let's be generous and assume that safrole is ~4% of the total weight of sassafras. That means that if I drink 1 root beer a day, I'd be 1/10th (4%/42% is ~1/10) of the TD_50 dose! (Alternatively, you could say I'd have to drink 10 root beers a day to get to TD_50). If safrole is as toxic in us as in rats, i'd be at nearly 1/100th the TD_50 dose. Now, granted, TD_50 means 50% chance of cancer. I don't want even a 5% chance of getting cancer. However, the probability of cancer falls quickly once you move away from the TD_50. The data I can find don't even look at the probabllity of lower doses of causing cancer, but if safrole behaves like other cancer causing compounds, 1/10th the TD_50 is likely to only cause cancer in fewer than 1% of us.
And remember, I've already probably over estimated how much safrole is in sassafras and how toxic the safrole is to us. Wikipedia
indicates that the cancer-causing byproducts found in mice and rat urine are not found in humans after consumption, raising questions about exactly how toxic it even is to us, if at all.
Let's not go too far and say that safrole doesn't cause cancer. It does at the right dose
But I think that dose is waaaay higher than you're likely to get. Pollution in the air, chemicals in your kitchen cleaning products, etc, will probably give you cancer first.
So, I am not at all afraid to use raw sassafras in my root beers, and I don't think you should be either.
What do I think the real reason for why the FDA was so quick to act against Safrole? It's one easy chemical reaction away from MDMA, the banned drug most of us know as ecstasy. By eliminating the food needs for sassafras, the industrial production sources all disappeared, making it very hard for an illegal drug house to get enough sassafras to make MDMA.
I'm interested to hear other opinions out there, and especially interested in reading any other sources people can find.