Two flaws. First is that being ignorant of data is not inherently racism. Many people think recycling plastic and glass is good, but the reality is that we probably should not be with our current methods. That is ignorance. Now, ignorance can lead to malice and when that happens for race it becomes racism. What is likely happening in my opinion is that letting in people that would not otherwise be here increases the incidences of crime even though the rate goes down. So, if you have natural born citizens committing at a rate of 3/100, and immigrants commit the same crime at a rate of 1/100, then you will have more incidents and less of a rate. This is the lesser point though
Good thing that is your lesser point, because it's pretty weak. A POTUS has no excuse making statements about crime among an immigrant population
in ignorance of the actual data and statistics kept by an agency of the executive branch over which he presides.
Not only is there no excuse, but likely there is no actual ignorance either. Trump has undoubtedly been briefed on the statistics, if not by someone in his campaign, then by someone in the White House. I refuse to believe he doesn't know. He is likely making his case with anecdotes knowing that it is wrong but that his base will accept the anecdotes and believe it anyway because they are predisposed to.
The second is that his statement does not imply that immigrants tend to be criminals. He is saying that if you let in everyone, regardless of how bad they are, then you will get an infestation like MS13 is an infestation. People often speak in imperfect ways, but, saying they and then saying like MS13 after saying "no matter how bad they might be" shows an attempt to split them between okay and not okay. I get that you probably will disagree, but had this been said by someone other than Trump, it would be easily defensible. If you want to say that technically he said something wrong because of the technical meaning of his words, then it should stand alone. If you have to bring in his past, then you have to admit that the words do not inherently convey what is being argued.
If you let immigrants of any national origin in, you will bring more crime, and including possibly some individual gangs or other kinds of criminal conclaves. Like the entire Russian mob, for example. So what? Total crime is irrelevant. Crime per capita is the only thing that actually matters, because that is what determines, you know,
your actual chance of being a victim of it. Compare a tiny island nation with 1000 people in it where 50% are felons to a nation of 1 billion people where 1% are felons. Which one is the more dangerous place to live? I think even an 8 year old would get the correct answer to that one.
Since the logic of "more immigrants equals more total crime" is transparently absurd if the
rate of crime isn't higher among these immigrants, I can only assume he means that the rate is higher or else what coherent point is he even trying to make?
So far as "bringing in his past," I don't think that is necessary. The only thing that is necessary is that we know this is the POTUS making the statement, because at least a little context is needed. Yet, we will of course consider his past. We're all like the jury who saw the evidence that was subsequently ruled inadmissible. Our collective bell has already been wrung, and it isn't going to unring because you want to rule certain things inadmissible for purposes of discussion.