So what jkane? Most traders are uninformed when they start out - they blow up their spreadbetting accounts within a few weeks. But not because they're using spreadbets, its because they don't learn the craft, partly becasuse they think its easier than it really is. If they don't get past this, they would blow up whatever vehicle they used.
Its not wrong to be ignorant, but it is dangerous to stay ignorant.
First, your statement is factually incorrect: it doesn't override it every time. It overrides in some people's circumstances but not in those of others, depending on several variables. What matters, in this context, to a professional trader is the overall cost of doing business. There are large numbers of people whose overall costs are reduced, and their profits therefore increased, by using spreadbetting. This is simply factual and incontrovertible.
Secondly, throughout this thread and in countless other posts you've made in this forum, your perspective is "informed" by out-of-date beliefs you have about the sizes of the spreads and a lack of consideration about what you're comparing them with. In some circumstances you're quite right that the dealing-costs will be higher for those using spreadbetting (e.g. than for those dealing directly, in size, in an underlying market). In other circumstances (and these are exactly the circumstances of many members of this forum), the spreads are not necessarily higher when compared with trading via (for example) a retail forex broker.
There are threads in this forum from as long as a decade ago in which the perceptions you so regularly display here are debated in detail, with carefully worked illustrative examples proving them to have been mistaken, ill-informed and prejudiced even as long ago as that. They still are now - and all the more so, in fact. It's very easy to imagine that one is "thinking through an issue" when in reality all one's doing is re-arranging one's own prejudices.