No fat is not simply fat... there are lots of different types
Saturated fat is the evil type which raises the LDL (L= Lethal!) cholesterol in the body and can lead to heart disease. Butter is very high in saturated fat compared to other spreads.
As a generally guide, the harder the fat (e.g. butter/ lard) the higher in saturated fats.
Other types of include Polyunsaturated (found e.g. in sunlower oils) and Monounsaturated fats (e.g. in olive oil). These have been shown to have a less detrimental effect on LDL cholesterol levels, and in some cases a POSITIVE impact in raising HDL (H = 'healthy' or 'good') cholesterol in the body.
What muddied the waters historically was that margarine was often produced using a process called 'hydrogenation' which used to create 'trans fats' which actually had a similar negative effect as saturated fats,
However a few years ago most spread manufacturers changed their processes to stop doing this, so you'll find very few of the mainstream (soft) spreads have them any more. Also, many of them lowered the total fat in their products so it is often only 60-70%. By law, butter has to be 80% fat to be called 'butter'.
Like someone said earlier, what you choose depends on what you're after in your diet really. If you eat very little butter and don't use it for cooking etc then you'll probably be fine. If you want to lower your fat intake as part of a diet then steer well clear.
If you have a history of raised cholesterol and heart disease in your family opt for a sunflower spread - especially a lower fat one.
In our house we only use a tiny bit of butter for breadmaking, other than that it's Olive Spread for toast etc and Low Fat Flora for sandwiches for me.