I agree with David on this. In commercial radio it is important to not only have listeners but to keep them listening. When a listener is always tuning away when they hear something they don't like you have low time spent listening levels. What this means to advertisers is they have to buy bunches of spots to reach the audience. Since agencies work a formula cost based on the market, the difference is what you can charge per spot even if you can get on the buy sheet.
In non-commercial radio, since Underwriting is based on the number hearing the message and since listeners that truly love the station are the only ones that might consider donating, the listener that hears a something they don't like with any level of regularity, does not donate and eventually decides the station is not their cup of tea.
True, long established alternative stations seem to do well, but newer stations in the format seem to struggle and the 'ramp up' time seems to be very long. When you have a 1 share and a TSL of an hour and 15 minutes a week after two years or more, you can bet board members or investors are starting to doubt things. You simply have to hope you have a good small support base to keep working it. Naturally in a top 10 market, a 1 in a lot easier to monetize than a 1 in, say, market #50 because the bigger number you reach, the greater number of those 1% you have.
The real issue for the format is how the audience has splintered. Think back to top 40 in the late 1980s. One group liked Hip Hop but the rest didn't. One group liked Rhythmic but the remainder didn't. One group liked the more rock based tracks but the remainder didn't. The top 40s that survived had to morph away from playing it all to just playing some material and that greatly lowered the numbers they achieved only a few years prior to this. I literally saw top 40 go from a dominant format to almost a non-existent format over about a 5 year period. It was sort of a generational change although top 40 had always been 'evolving' from the pre-British invasion, the rock influence, the Adult Contemporary dominance, eventually with Disco and a few years later with 'New Wave' but there were enough core artists to prevent a full takeover of the format. While there was a group that disliked every change along the way, the idea of playing the biggest selling songs still worked. When the biggest selling songs were so diverse that the core audience did not like a fairly decent percentage of the songs, the heyday of top 40 as we knew it, died. I see the same happening in the Alternative format. The question is if each subgroup is substantial enough for radio to serve them. I suspect it will all pan out in a few years.