I think it's a totally respectable position to say that the US should take no military action against Assad, because the alternative is worse. Meeting with him also isn't necessarily something that I'm against. My problem with Gabbard is more that she went to Syria and spoke with a bunch of Syrians in Assad-controlled territory (and thus, presumably people vetted by Assad), then came back and repeated Assad-approved propaganda about how all the rebels are the same, without any consideration of the fact that she might have been getting a skewed perspective by only talking to people in government-held territory. I discussed this back in January:
Assad is the lesser evil compared to ISIS
He's still, y'know, evil.
He's a horrible person, no doubt, but I'd rather have him run things than ISIS.
But Gabbard hasn't simply said he's better than ISIS. She's gone on a trip to Syria in which she (apparently) only visited Assad-controlled territory, and talked to Assad-approved Syrians, then came back to the US, seemingly believing everything they said. No acknowledgement in her commentary of Assad's crimes, or that Assad might be manipulating the stories she was hearing on this trip.
E.g., here is what she concluded after talking to the make-believe opposition in Damascus:
