Pace
Semantics perhaps but you have LESS control than with the engine running for the reasons you state. A glider never had an engine in the first place (well most anyway) or the space shuttle (after re-entry) so they haven't "suffered" any change in the control.
The current philosophy among Cirrus pilots is that a conventional forced landing should be the exception, not the rule. Why? Well as I said earlier if you fly regularly with PPLs and "surprise" them with a simulated engine failure most don't make a very good job of things. Moreover the evidence of a good outcome following a chute deployment is very good indeed. The trouble with a conventional forced landing is that however good you are there is always the possibility of the unexpected. There are many cases of pilots failing to spot power cables, large boulders or other obstacles all of which can really spoil your day.
I am aware this topic has been done many many times before and both views are regularly expressed but I can only report the current consensus. Of course if you fly a Cirrus, are in current practice of FLs and there is a socking great big field presenting itself to you are going to carry out a conventional FL - I would at least. As the field gets smaller, the terrain more hostile and you face up to your current gliding skill levels the chute becomes ever more attractive! From my own point of view I am conscious of the dangers of indecision - if in doubt I shall be opting for the chute!
As to the original question the risk of an engine failure is very small, the risk in a twin of a double engine failure while not half is not far of. The point comes at which the risk of not carrying a chute are out weighed by other factors. For me that point is reached with a twin, but I am a firm believer that it is a worth while addition in a SEP.
All the best.