'Unsafe' is quite nebulously defined w.r.t. radiation. There is a level below which statistical noise makes it impossible to determine empirically whether anyone dies or suffers serious adverse health effects from radiation exposure, and the 'safe limits' are well below this level. It is conservatively approximated that deaths and serious health effects continue linearly into this range and only reach zero at zero exposure. But there's no evidence for this - it's just a sort of upper-bound adopted because everyone is jumpy about nuclear power - and good reasons to think it isn't true.
Even ignoring that, and accepting the conservative estimates of adverse effects, even an accident like Fukushima is causing quite marginal adverse health risks. The sort of stuff that is routinely ignored when it comes from other industrial pollution, cars, drinking alcohol, not wearing a helmet when you go cycling, etc. Or, actually, quite a lot smaller than those things. People radically overestimate these risks while happily accepting larger risks in their day-to-day life. In other words, should Japanese parents be giving their children face masks, etc? Essentially no - this is a long way down the ladder of greatest potential health benefits to be gained from inconvenient mitigating behaviour. But psychologically, it's difficult not to, because society doesn't really care that much about a few kids drowning in swimming pools or hitting their heads when they fall off their bikes, while low level radioactive contamination is considered much more sinister even if the real risk involved is actually much smaller.
To the wider point of potential better sources - fossil is pretty much better if you don't believe in AGW, although these also release pollutants - sometimes including radioactive pollutants - that have a similar order of magnitude health impact to Fukushima, ie. extremely low, but possible to assign a finite number of deaths to. If you care about one, you should care about the other. Also, we are reliably informed that AGW is real, which knocks fossils way down, especially for an island country like Japan that has a lot to lose from large scale warning.
'Alternative energy' is nebulously cited - what alternative? Nuclear is the only source that can economically and practically take up the whole, or even a large part of national-scale generation. Since they mention politics, "the left" is simply sticking their heads in the sand on this issue. Don't want CO2, don't want nuclear, have no alternative that stands up to scrutiny. Do you want to devolve society to pre-industrial levels? Nuclear, even with occasional accidents, is a lot less damaging than that. Do you want catastrophic warming? Again, I'd take 10 Fukushimas before I'd take a 10m sea level rise, if I were living on the coast of Japan.