There are a lot of legitimate criticisms of papers that get removed, including comments that suggest sub-optimal experiment design, overreach in conclusions, or statistical issues (which are usually present in the hard-hitting, catchy studies that make it to r/science). Normally, these are part of healthy scientific discourse.

When the moderators of r/science particularly agree with a post or it is politically charged, almost any discussion of the actual science involved is purged (unless it is praise or an "explanation" that includes a lot of praise). When the mods don't agree, you can see some discussion of gaps in papers, but you must take the conclusion of the paper as 100% true, which is not how science works.