Downvotes are an unavoidable effect of having an answer that is not accurate, and they should remain that way. Downvotes are not a criticism on the poster, they are the way to keep good answers on the top and inaccurate answers (duly indicated as such in the comments, ideally) further down; it's what makes this site good.
One strategy to answer questions is what you describe: post what you know and let the community tell you when it's wrong. In that case, you should be prepared for exactly that: the community will tell you it's wrong by downvoting it. If that happens, the onus is on you to figure out why and to fix it. You can politely request explanations for the votes, and if your tone is right then people will stop by and help, but they are not obliged to. Drive-by downvoting hurts but it is necessary and has been gone over a million times in this and the mother meta.
If you want to avoid those downvotes, the answer is simple: don't post inaccurate answers. If you're not 100% sure of the material you're posting, do your homework, investigate, check, and revise whatever needs revising, before you post. This is, I feel, how many of us approach answers, and it has the huge advantage that it lets you learn while you answer. Indeed, it is probably the reason many of us are here: we learn by answering.
Finally, as jinawee pointed out in a comment, lifting text straight out of different sources without proper attribution is straight-up plagiarism and should be removed from the site if present. If you find text that looks 'taken out of a textbook', google it and find out. If you do find such an instance, the correct procedure is to edit the post yourself: include links to the original sources, and indicate whatever text has been copied by the use of inline quotation marks and quote blocks for longer stretches. Do this regardless of the poster's reputation, and particularly so for high-rep users, who should know better.
That said, I do not think anyone does this and have never seen an instance on the site. Most people do type all of that. They either know it already - which is exactly what we want, a site where experts can take fifteen minutes to explain what they know and save you many hours of research - or they find it out, in which case they learned as much as you did in the process.