contacttower118.2, speed control is not an essential part of getting an aircraft on the ground (unlike, say, descent), it is simply one of a range of controlling techniques that are available to the controller. Of course, some well organised high traffic density airports will rely on speed control to a great degree in order to squeeze every ounce of capacity out of the airspace and approaches. In other circumstances, however, speed control may be applied if it suits the particular traffic situation.
Speed control should be like any other ATC instruction - comply with it or tell the controller if you can't. It's no more important than any other instruction or type of instruction - it will have been issued to maintain separation or for sequencing.
If it appears that speed instructions are routinely being applied arbitrarily by some units maybe a word through your Ops Management to the unit concerned might either resolve the problem or provide a reason.