https://pubmed.ncbi.nlm.nih.gov/27251151/

Some passages:

>More direct evidence demonstrating that canola oil and soybean oil - 2 major vegetable oils consumed worldwide - differ in their effects on markers of DM in rats is shown in figure 25. In the figure 25, the 19C (19% canola oil) group showed higher insulin resistance (HOMA-IR) and more damage to pancreas β-cells than the 19S (19% soybean oil) and 7S (control) groups. The 19C group presented lower percentage of pancreatic islets area in comparison to 19S (-41%) and 7S group (-70%, p < 0.0001) [51]. DM patients in Japan are characterized by exhibiting both insulin resistance and impaired insulin secretion. This animal study is the first to demonstrate that a common vegetable oil, accounting for more than 40% of vegetable fats and oils consumed in Japan, impaired pancreatic function to secrete insulin. Similarly, these 2 vegetable oils differentially affected oxidative stress-related enzymes in erythrocytes and vascular properties in the SHRSP rat [52].

>Despite the palatability of palm oil, its safety has not been established even though many articles from exporting countries emphasize its safety. For example, palm oil unusually promotes mutagen-induced colon carcinogenesis comparable to high-linoleic safflower oil, using perilla oil as a control (fig. 31) [61]. The difference in the rate of carcinogenesis between perilla oil and safflower oil has been explained in terms of the n-6/n-3 balance and the established concept of the arachidonic acid (ARA) cascade promoting carcinogenesis. However, given that the linoleic acid content of palm oil is very low, unidentified minor components must be responsible for the unusual cancer-promoting activity observed. Similarly, olive oil increased mutagen-induced aberrant cryptic foci in rats [62], and the involvement of minor components in olive oil is suspected given that oleic-rich safflower oil with a fatty acid composition similar to that of olive oil does not promote carcinogenesis [63].

>Fig. 31

>Unusual cancer-promoting activities of palm oil and olive oil in animal experiments. Data for palm oil (left) are from Narisawa et al. [61] and those for olive oil (right) are from Onogi et al. [62]. Refer to figure 22 for the fatty acid composition of vegetable oils used. In the left figure, * p < 0.01 vs. other groups. In the right figure, * p < 0.05 and * p < 0.01 vs. olive oil group.
http://www.karger.com/WebMaterial/ShowPic/509075

>In addition to its cancer-promoting activity (fig. 31), palm oil was shown to shorten the survival of mice [64] and induce hyper-insulinemia in rats [65]. We strongly argue, therefore, that increasing the supply of palm oil as an alternative to industrial trans-fat is not a safe path to take.

Regarding your point about omega 3 and 6: yes, they are necessary, but that doesn't make vegatable oil "good." Additionaly, there may be too much omega 6 in many vegetable oils:

>thus, it is not the saturated to polyunsaturated ratio but the n-6/n-3 ratio of dietary lipids that is crucial for the prevention of CVD, DM and several other elderly onset diseases [39,58,70] as Bibus and Lands [94] recently reviewed. Currently, people in industrialized countries generally ingest several-fold more linoleic acid than is essential (0.5% of energy) and the intake of n-3 fatty acids is relatively deficient. The more than 3-fold higher CHD mortality in the US as compared to Japan is likely to be due to the higher n-6/n-3 balance of ingested foods in the US.