Security doubts on 3DES default

[Ryru]

Hello List

I'm new to this list and joined because I have some security doubts
regarding encryption preferences (setpref/showpref).

According to the gpg2 man page, 3DES is added always as kind of least
common denominator:
8<---
When setting preferences, you should list the algorithms in the order
which you'd like to see them used by someone else when encrypting a
message to your key.  If you don't include 3DES, it will be
automatically added at the end.  Note that there are  many  factors that
go into choosing an algorithm (for example, your key may not be the only
recipient), and so the remote OpenPGP application being used to send to
you may or may not follow your exact chosen order for a given message.
It will, however, only  choose  an  algorithm that  is  present  on  the
preference list of every recipient key.  See also the INTEROPERABILITY
WITH OTHER OPENPGP PROGRAMS section below.
--->8

In my opinion this design decision can lead to serious security
troubles. If someone, knowingly or not, removed all his/her symmetric
encryption algorithms in his/her public key, our conversation would only
be 3DES encrypted.
In a situation in which there are several recipients, e.g. a encrypted
mailing list, one participating public key/person can downgrade the
whole encrypted conversation to every recipient to 3DES instead of lets
say AES256.

I think the same goes for the hashing algorithm SHA1.

Is my understanding correct or do I miss an important fact? What are
your thoughts about this behaviour?

Wouldn't it be great to raise the minimum encryption and hashing level
to a more secure cipher?

Thanks in advance and best regards
Pascal