Did he do a good thing? No. In the first place I don't care that they were "evil" lawyers; they were human beings.
But even if you want to consider whether they "deserved" it: some, like Holland Manners, were directly orchestrating and taking part in plots which got innocent people killed as Angel pointed out. Others were just sheep following the herd until pay day to put food on their tables. Do we have the right to judge them for being followers during reigns like Holland's? Yes. Kill them? No. I've always thought W&H, with the exception of the Senior Partners and the other key players, was a study in the grey areas of morality and just how far human beings are willing to go to survive in any climate. It's bleak, sure. But look at Ats season 5. When Angel is CEO, he supposedly gets the entire firm operating in the direction of the good, like a well oiled machine. And sure they're different employees by the time that happens after the beast had killed the former ones, but where do you think the Senior Partners found them? Same place as they found all of their other employees. In short, having W&H in the show serves to remind us that people can be manipulated to do both good and bad things depending on what will serve them best. It takes heroes to say no sometimes. The lines aren't so clear in the real world; it's not "do this and someone dies," but there are decisions to be made which could hurt or harm fellow citizens of the Earth, and humans aren't immune to overlooking these things as we well know. I believe that this is the unpleasant truth which the writers were hoping to represent, (albeit on an extreme level), with the lawyers at W&H.
So considering all that, it's of course horribly wrong and immoral that Angel would directly allow Dru and Darla to kill human beings. Angel would tell you that himself, and so would the people who respect him the most.