Perhaps 'dangerous' is too emotive and vague a term to be bandied around in this context - branding something simply as 'dangerous' or 'safe' is too binary when we all know there is a sliding scale of risk attached to aviation (as in most things in life).
So if you start with the premise that all aviation activities carry risk - which we make strident efforts to minimise through training, regulation, engineering practices etc - it is clear that some of those activities will carry additional risk.
Is flying close to the ground inherently 'dangerous'? clearly not becuase it is happening around the world all the time. Does it carry extra risk? Most certainly, or we would all be smashing around at 5' and 140 kts because that would be lots of fun.
However, most of us want to go home to our wives and family at the end of the day so such additional risks as wirestrike, inadvertant contact with the ground, birdstike, catastrophic mechanical failure (including engine failure) are taken into consideration and the sliding scale of risk (in this case lower and faster) is modified by our willingness to take on that extra risk and our reasons for doing so.
The message really is - can you fly inside the H-V curve? Yes.
Should you fly inside the H-V curve and how far into it do you go? Providing you have understood the additional risks and have a good reason for doing so then how far you push is a matter for a good risk vs reward assessment.
The danger is that pilots often have a greatly over-inflated opinion of their ability, especially in dealing with rapidly changing and dynamic situations and that is where people get suckered into the 'I can do this, I'm a great pilot' which can often become 'I've been doing this for years and it's been fine' right up to the point where it isn't.
The Colin Macrae incident is a case in point - over confidence and a history of showboating isn't a good recipe for safe low flying.