Bryan Caplan has an interesting discussion of what he calls "liberal conflation". The discussion wanders, but it seems pretty clear that he is frustrated by how many different views political philosophers call "liberal", he wants to think more narrowly about what we call "liberal", and he wants it to center on some sort of libertarianism. I think he is unnecessarily bothered by this. Caplan is thinking about this in partisan/ideological terms when I think what we're really talking about is a political-philosophical school of thought. From an inherently partisan perspective, of course it seems weird to "lump almost everybody together". From a philosophical perspective this really isn't as problematic.
I see "liberalism" as having a few guiding tenets, including:
1. Individualism - individuals have agency and responsibility distinct from the collective, and they are equals.
2. Negative rights - liberalism is at its base a philosophy of negative rights
3. Freedom - the idea that individuals should be free from coercion
4. Secular, representative, government.
5. Tolerance and pluralism.
6. Private property rights, protected by law.
It's just a list off the top of my head, but I don't think it would be too controversial and I think it covers all the bases. As a philosophical framework, this does have a lot of adherents, at least in the West. But as a philosophical framework, I think it also has to be considered a general foundation rather than a specific or partisan creed. For example, some people put stock in the idea of positive rights as well as negative rights. I'm extremely skeptical of that for all the canonical reasons for being skeptical of positive rights, but I don't think that automatically disqualifies them from being considered "liberals", although that idea itself is not a "liberal" idea. Libertarians are quite good on 1., 2., 3., 5., and 6., but they often at the very least day-dream about (if not actively pursue) sabotaging 4. if there are ever any tensions between 4. and the other tenets. And this point about "tension" is an important one to raise. There are tensions in liberalism precisely because it is a broad philosophical disposition, rather than a partisan position with a platform that can be crafted to minimize internal tensions.
As I've stated on this blog many times, the ideal of 6. is imperfectly implemented in life (and certainly the same can be said of any of these). That leads to tensions between an imperfect implementation of 6. and the ideals of 1. and 3.. My freedom (number 3.) is imposed upon by polluters precisely because 6. (private property rights) has never been and probably can never be perfectly implemented. What is the "liberal" solution? There is no clear liberal solution (this would be a problem if "liberalism" were an ideology). One of the important things about liberalism is that when all six tenets are reasonably well respected, society has a tendency to right itself. The free market is by far the best example, but in more complicated cases like pollution externalities, 4. combined with 5., tempered by reminders of 2. can come up with a solution where 1. and 3. alone might not have been able to. So "liberalism" is an extremely robust philosophical disposition in that sense. But when you start privileging or removing any of these elements, it becomes less robust. This is one of my biggest concerns about libertarianism - not an error of commission so much as an error of omission.
So does this "lump everyone together"? It does and it doesn't. If you restrict the analysis to the West, it lumps an awful lot of us together. But there is differentiation - libertarians stress some elements, "progressives" stress others, and "conservatives" stress others. I think it is quite a strain to fit "socialists" into liberalism, unless we're talking about distinctly non-Marxist/non-Leninist socialists (and even these have pruned liberalism down).
I think the other thing to keep in mind is that this is only even on our radar as a "conflation" because the alternative has been so decisively destroyed so recently. A very popular illiberal political philosophy fell only twenty years ago. That isn't that long ago, and a new one may still emerge. Why splinter victorious liberalism just to pick an internecine fight when in a matter of decades there might be a new challenge? Former illiberal socialists are turning into liberals in droves, and libertarians want to shun them because they want to hijack liberalism and make it in their own likeness? I don't see the point, even if I were to sympathize more with libertarianism.
And what challenges could emerge? Well, with the improvement of data collection and information technology we shouldn't write off illiberal socialism just yet. People could easily come back to the opinion that they can plan society as technology develops. And what's even more scary is that they probably could fake it longer and more successfully than the Soviet Union did. It's doomed to failure, of course - but it could gain adherents. Pre-modern fundamentalism is presenting an increasing challenge to liberalism in many quarters of the world. If any of these threats become more formidable, "liberalism" is going to look less and less like a conflation to Caplan.
Part of me was simply frustrated when I read Caplan. "Liberalism" if anything started with 1., 4., and 5., with 2. being added as 4. and 5. became better defined, and 3. and 6. added as market capitalism began to emerge out of economic nationalism and mercantilism. If 1. and 4. form the basis of "liberalism" (which I think they do), it's not clear at all why libertarianism is the "first among equals" or the "true" liberalism. The more libertarians try to make these claims for themselves, the more someone else is going to get frustrated and push them out of the club (Caplan points out that "modern liberals" have a lot in common with illiberal socialists, but by the same token couldn't we say libertarians have a lot in common with illiberal anarchists?). There's good reason to be frustrated with Caplan in this way - he makes some pretty bad arguments. However, I think the best way to tackle this "liberal conflation" issue is simply to remember that this is a philosophical disposition we're talking about - not an ideology. An ideology that everybody buys into is indeed diluted and might require some purges. A philosophy that everybody buys into, on the other hand, is probably just a very sensible philosophy. After all, Bryan Caplan is well known for aruging that we should limit the franchise based on a person's economic and policy enlightenment. I don't get as apoplectic over that as some people - I can respect speculative, out of the box thinking. But it seems rather strange that an advocate of limiting the franchise should be so bold in claiming the liberal mantle.