If you pitch it directly to the team who have (most likely) done their own homework about moving to micro services, that it is not a good decision, even though your point could be valid, may not be well taken as it can subconsciously be interpreted as you being non-consensus driven/jumping to conclusions.

Why not: 1. Draft an email with a subject 'Second opinion on moving to micro services 2. Let the email body be a very succinct description that a. you have done some research, b. you respect the team's decision but c. would like their opinion on your research. Also seek a time for a 30 minute presentation and 30 minute feedback/discussion. Don't send your document with the email, keep that for your presentation. That way you will be seen in positive light, as a team member with his own opinions but also a team player.

Also, have you asked them what was the data from their research that made them take the decision to move to micro services?