Here is a simple demonstration. Consider the conservative argument that when you raise the minimum wage, elementary economics of supply and demand results in fewer jobs for poor people. I guarantee you that if you present this argument to 10 liberal friends, more than half will have a strong emotional response against it. While responding, some are likely to turn an interesting shade of red. Yet there is no intolerance in that argument.
Furthermore the argument is fairly well grounded in reality. Supply-demand curves are well-established basic microeconomics. And furthermore if you play around with https://fivethirtyeight.com/features/science-isnt-broken/#pa... you will find that Republican policies (which include low minimum wages) are consistently better for creating jobs. Just as Democratic ones are better for increasing GDP.
Of course some liberals will have emotional reponses to something that is not actually an intolerant opinion, like your example. There is no admission requirements to be a 'liberal', so we can't deny entry to people who don't understand the difference between a moral question and an implementation question like minimum wage.
The fact that a liberal thinks that "conservative" should be replaced with "intolerant" is a symptom of the problem that I describe.
You probably don't really think about the times a liberal person is reasonable and logical. You certainly will remember the ridiculous liberal who says illogical things.
Might that be skewing your impression of what 'most' liberals believe?
The statement that I made about minimum wage has the effect that I describe because it is a major liberal-conservative argument. As soon as someone states a position on raising the minimum wage, everyone else around will tend to assume that they know their political position. I could have produced other examples ranging from approving oil pipelines to the wisdom of tax cuts to cost effective ways to produce health care.
Now you may be atypical. But most liberals/conservatives respond with the same pattern. They figure out whether you're with/against, and then respond emotionally. And the issues do not neatly divide on "intolerance".
More interesting, the dividing issues change over time. Today woman's rights is obviously a liberal issue. If you go back 100 years, allowing women the right to vote was just as obviously a conservative one, because women were a reliable vote for Prohibition, which was a thinly veiled tool to attack blacks, Jews, Irish, and other "undesirables". You can thank the KKK for helping women get the vote in this country.
The dividing line really isn't as simple as it seems at the moment. But it is sometimes easier to see this with the perspective of history.
> as a premise is certainly internally consistent.
Karl Popper argued that, in fact, that exact rule is not just consistent but necessary for tolerance to exist:Upvoted for bringing it to my attention, though. :-)
That's a clever slogan. But the logical response to that would be to say that liberals are tolerant of everything except intolerance.
Which as a factual statement is of course arguable, but as a premise is certainly internally consistent.