Plant foods don't have Vitamin A (Retinol); they have β-carotene (beta carotene), which gets converted to Vitamin A, but this process is not very efficient and as a result, the vegan diet is at risk of being deficient in vitamin A. This study is cited
This isn't a good justification that one "might" be deficient in a vitamin that now we need to partake in an unethical act. You could just improve your diet. The fact that a poorly planned diet of only Skittles and beer lacks some nutrients doesn't mean that all vegan diets are suddenly unhealthy.
The study had 7 participants which is not enough for an epidemiological survey (which it was never intended to be), and therefore epidemiological data cannot be inferred from it. The study is intended to take a look at the rate of vitamin A conversion at higher doses than humans would consume. Hence the conclusion of the paper states that "Thus, dietary intakes are likely to be similar to or lower than the doses studied here, and it is possible that conversion of β-carotene to vitamin A is less limited at smaller doses.... These results explain why vitamin A toxicity is not observed in individuals consuming large amounts of β-carotene"
So to then use this study to discuss deficiency is not scientifically sound, since the data in this paper were collected in surplus, not in deficiency, and the paper itself states that retinol conversion decreases as your body reaches saturation.
If you wanted to demonstrate that you couldn't get sufficient vitamin A on a vegan diet, then you should cite epidemiological data, not postulate about what potentially might or might not be healthy in the absence of such evidence. Unfortunately, the data do not support this, as, for instance, these three papers (1, 2 - the top three results for "plasma retinol vegan" on google scholar) demonstrate that vegans have blood vitamin A within the reference range, and an abundance of β-carotene, hence they are converting it at lower and lower ratios as their bodies have enough vitamin A already.
The RDA of retinol is 900ug. At a 13:1 conversion ratio, the RDA of β-carotene is therefore 11700 ug, which is found in only 141g of carrots (a small pack of carrots at your local grocer) or less than half a cup of sweet potatoes. Other foods are directly fortified with vitamin A. So there's no reason to suggest that a vegan diet cannot get enough vitamin A.
Hypervitaminosis A is actually a very serious condition, so this is actually a good thing, that your body doesn't convert more of it than required.