Would you as an early retired parent feel pressured to help pay for a fancy wedding and honeymoon if the fiancee's parents paid a large amount also?
No. I wouldn't feel pressured to do it if I was still working either.
Look. It is your money. No one can pressure you to do anything with it unless you want to be pressured. I am not one of those people who feels that only the bride's family should pay. That harkens back to an old fashioned patriarchal system that I don't believe it.
That said, I don't see why parents get involved in any of this at all. People aren't getting married at 20 anymore. Usually both participants have been out in the world and are supporting themselves. That includes paying for their wedding.
Now - some parents want to contribute something to it. That is fine. Bride's parents can knock themselves out. I will say that $50k would not come close to covering what is planned so one of two things is going on. Bride's parents have set their own limit (which is fine) and bride and groom are trying to make it happen through upping your limit. The other possibility is that bride's parents are wanting this as well.
Resist. Don't do it. Find an amount that are happily and easily able to afford. Offer it to them as either part of the wedding planning or as a gift. Let's say it is $10000 (made up number that could be whatever). If you contribute nothing to wedding then give them the $10000 as a wedding gift. If you contribute $10k to the wedding then, well, that IS their gift.
Honestly, I also have to say I wonder about this marriage. The maturity of the participants seem questionable. Justifying stuff because "everybody else" gets to do X is an argument I expect from those in elementary school. I would put give no credence to such an argument and it would demonstrate such a lack of maturity that I would be inclined to offer very little to this enterprise.
By the way if you agree to write a check for wedding expenses I think there is a risk here that this wedding will not come off at all and your money will be completely wasted. Personally, I would not contribute to the wedding expenses. I would write a check and give it to them after the wedding. They can then use the money for whatever they want. Including paying bills for the wedding or honeymoon.
Do not consider placing yourself in financial jeopardy over this. Your son and his soon to be wife need to grow up.