Removing tariffs on beef specifically is a serious mistake, there's no need to incentivise any more production of that.
Other agricultural imports, like soy and coffee beans, are a huge boon to the EU on the other hand. If this results in cheaper coffee, everyone in my country, for one, will be ecstatic.
While I agree that we ideally shouldn't be incentivizing more beef production, the reality is that making a trade agreement (at least the European way) involves a lot of give-and-take, compromises, and concessions.
Mercosur countries have a powerful beef industry which they're proud of, and their governments are interested in advancing that industry. Lowered beef tariffs were almost certainly one of their prerequisites to forming a deal.
That said, do note that the tariffs are only lowered up to a quota level of beef imports. Relative to the size of the EU's domestic beef industry, these imports are not that significant.
We have to notice the blatant hypocrisy here: on the one hand we are told that the environment and net zero are top priorities, and on the other hand we are also told that it is great to have beef shipped to us from literally the other side of the world... (Tokyo is nearer to Brussels than Buenos Aires)
The process of shipping of beef from Buenos Aires to Brussels has a much smaller climate impact than the process of producing that beef in the first place. In particular, the methane burped up from cows has a gigantic impact on radiative forcing in the upper atmosphere. And again, the amount of beef being allowed to be shipped to Europe is quota'd to a quite amount relative to the domestic industry.
That's not to say that we shouldn't do anything about these emissions, but the solution is going to be to develop more climate friendly shipping techniques, not to eliminate global trade.
Beef from Argentina is basically as good as it gets in terms of animal welfare.
Most are raised under extensive systems (not confined feedlots). They live on large grasslands (hundreds of acres) where they roam freely and graze pastures.
That's completely unlike things like Chicken which live their whole life in over crowded poultry houses, never seeing the outdoors, or even daylight.
Soybeans have probably a worse impact on the environment than beef. Most of the deforestation in SA in the past couple of decades was for soybean farms.
According to this source, 77% of soy production is used for animal feed. That only a small percentage of it goes to cattle is irrelevant in terms of the damage caused.
Argentina beef are raised in pasture. About as eco friendly as it gets. Converting pasture to row crops is far more devastating to the environment (topsoil loss, GHG emissions from loss of biomatter in topsoil, fossil fuel derived fertiliser and more.)
Other agricultural imports, like soy and coffee beans, are a huge boon to the EU on the other hand. If this results in cheaper coffee, everyone in my country, for one, will be ecstatic.