https://joinmastodon.org/covenant is a very good idea in principle. It states:

Active moderation against racism, sexism, homophobia and transphobia
Users must have the confidence that they are joining a safe space, free from white supremacy, anti-semitism and transphobia of other platforms.

However, the current server directory includes many instances that do not suspend or silence known origins of targeted harassment and abuse. This means that users signing up on those servers may be opened to harassment and abuse shortly after signing up (possibly in a manner invisible to most users if it is done via "DMs", hate-follows, etc.). That's in direct contravention to the stated goal of the covenant.

I would propose to strengthen the covenant with the following (and to gradually apply that policy to the existing directory):

Moderators must also take action against servers from which harassment or abuse originates, by silencing or suspending servers which refuse or neglect to take action to stop it.

To be clear, I am not proposing to adopt an expansive definition of abuse in this context. Servers may have various codes of conduct to moderate behavior deemed to be obnoxious or problematic. However, as an entrypoint to the network, https://joinmastodon.org/ must ensure a baseline of moderation standards are consistently enforced, so that advertised entrypoints to the network are effectively walled off against instances that willfully perpetuate abuse and harassment of the worst kind.

It should, in short, not be possible as a newcomer to join a server through the official portal, which refuses or neglects to suspend or silence a server that willfully tolerates or even encourages severely abusive behavior.