The reason that an under-powered amp will be more likely to blow speakers is that people will want to turn up the volume. You will reach a point where the amplifier power supply runs out of gas and the output signal is actually clipped or "flat-lined". This flat-line DC current will ruin tweeters very quickly and could damage other parts of the woofers and crossovers.
It's always more healthy to get an overpowered amp so that you always have a clean signal output to the speakers. It's better to send a "clean" high powered spike to the speakers. They can handle a one time spike that is over their rated power easier than they can handle a "clipped flat-line DC". It's very easy to hear when the speaker reaches maximum excursion and you can just back off on the volume (and don't hit those levels again).
With amp clipping, it's actually harder to hear when this happens. You could be "hearing" a somewhat clean sound, but the clipping is occurring and slowly damaging your tweeter voicecoils.
It's always more healthy to get an overpowered amp so that you always have a clean signal output to the speakers. It's better to send a "clean" high powered spike to the speakers. They can handle a one time spike that is over their rated power easier than they can handle a "clipped flat-line DC". It's very easy to hear when the speaker reaches maximum excursion and you can just back off on the volume (and don't hit those levels again).
With amp clipping, it's actually harder to hear when this happens. You could be "hearing" a somewhat clean sound, but the clipping is occurring and slowly damaging your tweeter voicecoils.