I actually don't have a problem with selective education, but I do have a problem with our current system.
My dh is Dutch. In Holland they have a selective system which works. At 11 the children are streamed into about 5 streams. As far as I know, all 5 streams are on the same campus, it is possible to move from one stream to another (for a late developer for example) and there are different opportunities available in each stream.
The top stream (about 5 %) go to university. The standard uni course is equivalent to our Masters degree, and is for the truly academic, the professions which require that level of training eg doctor and lawyer.
The second stream goes on to a higher education system which is more like our university level, this includes teaching degrees.
The bottom stream is a very practical education, so by 14 there are opportunities to be an apprentice, for work based training, for proper skills training.
The most important difference as far as I understand it, is that the streams 3-5 are valued and properly funded. In the UK it would be seen as ''failing'' to be in stream 4 or 5, but this is not true in Netherlands, they see it as children needing a different type of education, but one of equal value. Far fewer children come out at 16 with no qualifications.
I have always thought that the problem with the grammar system was not the selective nature of it per se, but rather that there is no movement possible across the system and the lack in investment in the secondary moderns and technical schools (which were originally part of the system, but have now disappeared)