The legal world isn't as big as you might think, and lawyers can expect to run into a lot of the same other lawyers, judges, and so on for decades of their career. You're talking to a lawyer who used to do litigation. The legal world is a lot bigger than you think it is. My friends that still do litigation have never come up against the same lawyers twice in their careers. But we practice in a big city. If you're in Hoboken or Fargo, your experiences will obviously differ.
Taking obviously unwinnable cases is a quick way to get yourself branded as a toxic lawyer.
You're assessing cases as "unwillable" before actually knowing if they are winnable. There are very few cases that are "obviously unwillable" at the onset and with extremely rare exceptions, that "obvious" part is due to procedural defects in the case, like an expiring statute of limitation that precludes a lawsuit. And in those cases, if your client wants to keep fighting after being advised that the case is procedurally unwinnable, you pursue all appropriate legal avenues still available to your client (or even ones that are now precluded but could be granted at judicial discretion), because that is precisely what lawyers are paid to do, and other lawyers understand that and do not hold that against them.
Moreover, no case is "obviously unwinnable" on the factual merits before discovery. Hell, it's even possible to take a case that is "obviously unwinnable" after discovery and still win (and indeed, I got my first trial one month after the bar exam because my boss thought the case was "unwinnable" but would be good for experience. That client is walking around free right now because I won an "unwinnable" case.)
As for "toxic reputation", your behavior in court and in dealings is what gets you branded as toxic, not the cases you take, and that is true whether or not your cases are winnable.