They tend to be horrible even for ostensibly 'Democratic' reasons: Irish or Italian ethnic collectivists with a hard on for reactionary unions like the Teamsters. All these traits are perfectly Democratic - and perfectly abominable.
In the IBT's defense, it at least realized that backing Reagan in '80 was a bad idea the minute after it did so, and hasn't endorsed a Republican since. (Of course the Democrats aren't much better, but yeah, the IBT endorsed Nixon and Reagan, so...)
Anyway, it's perfectly logical for Democrats to have a positive opinion of Ronald Reagan, given that they're the real heirs to the policies he promoted, be they privatization (Obama's trying to gut the TVA after all), lowering the overall tax burden we impose upon the rich (perhaps not in terms of outright income taxation but in terms of actual taxation, that is, Capital Gains Taxation), sending American troops to any number of foreign lands at the behest of corporate capital, and sabber-rattling with Russia.