Michigan Rep. Peter Meijer - one of only 10 House Republicans to vote to impeach Trump - narrowly lost his GOP primary last night to a MAGA election denier. Where did the most of the money spent on ads supporting the latter come from? The Democratic Congressional Campaign Committee! See Meijer's essay on this above.
A few points...
Unlike some other primaries in which Democrats spent money promoting MAGA types against better Republicans, the result here was close. So the Democratic money might have been decisive.
This is a reprehensible strategy for all the reasons Meijer says. If you believe the MAGA election deniers are not just ordinary political adversaries, but threats to liberal democracy, you can't simultaneously help them win primaries in the hope they will be easier to beat in a general election.
As the case of Trump, among others, shows, MAGA types can in fact win general elections in closely divided areas, especially when it's generally a good political environment for the GOP. So the assumption they are doomed to defeat is often dubious. To put it more concretely, if you're a Democrat and you really think the MAGAs are a dangerous menace outside the range of normal political disagreement, you should prefer, say, a 50% chance of losing the general election to someone like Meijer to a 25% chance of losing it to the likes of his primary opponent. The latter may be better for the narrow self-interest of the Democratic Party, but the former is better for the future of the nation.
That said, obviously the principal blame here falls on GOP primary voters. No one (not even the DCCC) forced them to vote for these MAGA clowns. Primary voters were susceptible to the ads and other misleading claptrap because of their own ignorance and bias. I would stand to argue for structural solutions to these problems, rather than relying on improving the virtue and competence of individual voters, because I don't think the latter is likely to work. But being a bad voter is still unethical behavior, even if there is little government policy can or should do to change it.