How serious is the problem?
At the moment, the earth is facing a major ecological overshoot. That is, we use up renewable resources faster than they are renewed. According to the Global Footprint Network, the Netherlands has already exhausted its rightful share of the world's resources. Belgium makes it even more colorful: April 5. And this is another favorable picture, the result of the Covid-19 outbreak. Since 1970, the year when humanity first went 'red', the ecological footprint has only grown. So the problem is serious indeed. And livestock farming is an important part of this footprint, and therefore of the problem. 
A meat tax is not a good idea and for this reason
Animal protein is the most digestible of all protein types according to the DIAAS method, which is recommended by the FAO . Growing children in particular need animal protein. Even soy, the most complete vegetable protein source, is still incomplete. Soy also contains toxins that make raw soy poisonous and can only be rendered unsavory with the help of traditional techniques such as fermentation . Archaeological findings have also shown that the descendants of farmers are taller, stronger and healthier than the descendants of people on a vegetarian diet who often show deficiency diseases .
Rich parents have enough money to buy meat for their children and to grow them up healthily. Now poor parents have that money too, because meat is relatively cheap. A meat tax will not deter wealthy parents who like to eat meat. So the real target of the meat tax, which its proponents will never tell you, is poor people, who spend a significant portion of their disposable income on food.
With this meat tax, poor parents are forced to give their children toxic soy or even worse vegetable alternatives. As a result, they are more likely to develop chronic diseases in adulthood.
In short: the heartless meat tax should never be introduced, this amounts to the heredity of poverty and condemning the children of the poor to a defective body.
In vitro meat, a better solution
Better, the government gives substantial development subsidies to Dutch companies that develop lab meat, such as Mosa Meat. Cultured meat is many times less harmful to the environment in terms of ecological footprint. If the cost price can be brought below that of meat from live animals, and at the moment the cost has already fallen from € 250,000 to € 9 per hamburger, this is a better solution. 
1. Global Footprint Network, Earth Overshoot Day
2. Laure Herreman et al., Comprehensive overview of the quality of plant and animal-sourced proteins based on the digestible indispensable amino acid score, Food Science And Nutrition, 2020, DOI: https://doi.org/10.1002/fsn3.1809
3. Arlete M. Becker-Ritt, Antinutritional and / or toxic factors in soybean (Glycine max (L) Merril) seeds: comparison of different cultivars adapted to the southern region of Brazil, Journal of the Science of Food and Agriculture, 2004, DOI: https://doi.org/10.1002/jsfa.1628
4. Helen Thompson, Switching to Farming Made Human Joint Bones Lighter, Smithsonian magazine, 2014
5. Mosa Meat: From € 250,000 To € 9 Burger Patties, Clean Technica, 2019