Erik,

How much hysteresis do you think you need?

For the 25 years before there were MAX parts, everyone used something akin to the 1489, which uses only the logic level supply. That was, and continues to be totally sufficient. Nobody had noise problems resulting from inadequate deadband. No part of the circuit requires that its input be compared with -3 volts. The 1489's 1.2 volt max on Vil, which you seemed to have trouble interpreting, clearly indicates that you're looking for something that's not there. Do you really believe that any system you're likely to work with has more than 4.2 volts of noise?

This whole discussion about the negative supply, the MAX parts, etc, began with

http://www.8052.com/forum/read.phtml?id=115584

Clearly, all that was at issue was whether the negative supply was needed for ISP, and I think you'll have to agree that it's not. I think you can convince yourself of this if you simply omit the charge pump from a MAX232, by grounding its oscillator pin and omitting the charge pump cap's. If all you want to do is shout your probably erroneous opinion louder, then you can skip that step. Of course, you could just look at the spec's for the MAX232, where I doubt you'll find any support for that noise-margin argument.

RE